Sulfonated Lignin-Derived Compounds and uses Thereof

ABSTRACT

The present invention relates to novel lignin-derived compounds and compositions comprising the same and their use as redox flow battery electrolytes. The invention further provides a method for preparing said compounds and compositions as well as a redox flow battery comprising said compounds and compositions. Additionally, an assembly for carrying out the inventive method is provided.

This application is a continuation of U.S. Ser. No. 16/091,436 filed on4 Oct. 2018 which is a national phase of PCT Application No.PCT/EP2017/000461 filed on 7 Apr. 2017 which claims priority to EPApplication No. 2017000198 filed on 13 Feb. 2017 and EP Application No.2016000575 filed on 7 Apr. 2016. The contents of each applicationrecited above are incorporated by reference herein in their entirety.

In recent years, concerns resulting from environmental consequences ofexploiting fossil fuels as the main energy sources have led to anincreasing prominence of renewable-energy systems (e.g., solar- andwind-based systems). The intermittent nature of such renewable energysources however makes it difficult to fully integrate these energysources into electrical power grids and distribution networks. Asolution to this problem are large-scale electrical energy storage (EES)systems, which are also vital for the smart grid and distributed powergeneration development. Another important application of EES iselectrification of on-ground transportation, as the replacement oftraditional combustion engines with hybrid, plug-in hybrid, and pureelectric vehicles (EVs) allows for reduction of carbon emissions andfuel savings (Soloveichik G. L. Chem. Rev. 2015, 115, 11533-11558).

The U.S. Department of Energy has identified four major challenges tothe widespread implementation of EES: cost, reliability and safety,equitable regulatory environments, and industry acceptance. Thedevelopment of novel EES technologies capable of resolving thesechallenges is critical (Soloveichik G. L. Chem. Rev. 2015, 115,11533-11558). Redox-flow batteries (RFBs)—first developed by NASA duringthe energy crisis of the 1970's and currently entering a period ofrenaissance—are among the most promising scalable EES technologies. RFBsare electrochemical systems that can repeatedly store and convertelectrical energy to 30 chemical energy and vice versa when needed.Redox reactions are employed to store energy in the form of a chemicalpotential in liquid electrolyte solutions which flow through a batteryof electrochemical cells during charge and discharge. The storedelectrochemical energy can be converted to electrical energy upondischarge with concomitant reversal of the opposite redox reactions.

RFBs usually include a positive electrode (cathode) and a negativeelectrode (anode) in separated cells and separated by an ion-exchangemembrane, and two circulating electrolyte solutions, positive andnegative electrolyte flow streams, generally referred to as the“catholyte” and “anolyte”, respectively. Energy conversion betweenelectrical energy and chemical potential occurs instantly at theelectrodes, once the electrolyte solutions begin to flow through thecell. During discharge, electrons are released via an oxidation reactionfrom a high chemical potential state on the anode of the battery andsubsequently move through an external circuit. Finally, the electronsare accepted via a reduction reaction at a lower chemical potentialstate on the cathode of the battery. Redox-flow batteries can berecharged by inversing the flow of the redox fluids and applying currentto the electrochemical reactor.

The capacity and energy of redox flow batteries is determined by thetotal amount of redox active species for a set system available in thevolume of electrolyte solution, whereas their current (power) depends onthe number of atoms or molecules of the active chemical species that arereacted within the redox flow battery cell as a function of time.Redox-flow batteries thus have the advantage that their capacity(energy) and their current the (power) can be readily separated, andtherefore readily up-scaled. Thus, capacity (energy) can be increased byincreasing the number or size of the electrolyte tanks whereas thecurrent (power) is controlled by controlling the number and size of thecurrent collectors. Since energy and power of RFB systems areindependent variables, RFBs are inherently well suitable for largeapplications, since they scale-up in a more cost-effective manner thanother batteries. Moreover, RFBs provide a unique design flexibility asthe required capacities for any application can be provided usingtailor-made energy and power modules.

A well-established example of an RFB is the vanadium redox flow battery,which contains redox couples exclusively based on vanadium cations.Nevertheless, there is also a wide range of less commonly used inorganicflow cell chemistries, including the polysulfide-bromide battery (PSB).The wide-scale utilization of RFBs using inorganic redox materials ispresently still limited by availability and costs of the redoxmaterials. That holds even more so, whenever the redox materials arebased on redox-active transition metals such as vanadium, and/or requireprecious-metal electrocatalysts. Toxicity (and associated health andenvironmental risks) of inorganic redox materials (such as vanadiumsalts or bromine) further limits applicability of inorganic RFBs forenergy storage. That holds in particular when applying distributed,modular energy generation technologies that use (intermittent) “greenpower”, such as wind, photovoltaic, or hydroelectric power. Also, theincorporated materials may constitute overheating, fire or explosionrisks.

In view of the disadvantages of RFBs based on inorganic redox species,RFBs were envisaged with different organic compounds. Novel organicredox active species for large-scale use in redox flow batteries shouldpreferably be inexpensive, with high solubility and redox potential, andexhibit fast electrode kinetics. In early 2014, Huskinson et al.developed a metal-free flow battery based on9,10-anthraquinone-2,7-disulphonic acid (AQDS) (Huskinson et al. Nature2014, 505, 195-198 and WO 2014/052682 A2). Yang et al. reported on anorganic redox flow battery with 1,2-benzoquinone-3,5-disulfonic acid(BQDS) as the catholyte, while AQDS or anthraquinone-2-sulfonic acid(AQS) was used as the anolyte (Yang et al. J. Electrochem. Soc. 2014,161, A1371-A1380). However, sheer volume of needed energy storagedemands millions of tons of active materials. To date, only a smallernumber of organic chemicals are produced worldwide at such a scale(e.g., methanol, acetic acid, and phenol). Based on scale andavailability, the “ideal” redox flow battery for large-scale deploymentshould be aqueous and use highly soluble multi-electron (i.e. highlyenergy dense) redox active species that are readily available andinexpensive as electrolytes. Derivatized anthra- and benzoquinonessuggested as electrolytes by Huskinson et al. and Yang et al. arecommercially available; however, costly and elaborate manufacture of anyof them severely limits their broad-range, large-scale employment.

In summary, despite recent advantages in the development of rechargeablebatteries, a long-felt need exists for safe, inexpensive, easy-to-use,reliable and efficient technologies for energy storage that enablesdiversification of energy supply and optimization of the energy grid,including increased penetration and utilization of renewable energies.By to their unique ability to decouple power and capacity functions,redox flow batteries are at least in principle well suitable for largescale energy storage applications. However, development efforts have notyet achieved large-scale employment of RFBs.

Moreover, existing redox flow batteries suffer from the reliance onbattery chemistries that result in high costs of active materials andsystem engineering, low cell and system performance (e.g. round tripenergy efficiency), poor cycle life and toxicity. Thus, there remains aneed for novel electroactive redox materials, which are readilyavailable at low cost and exhibit reduced toxicity. Preferably, suchelectrolytes further provide for a high energy density, a high operatingpotential, increased cell output voltage and extended lifetime.Accordingly, there is a need in the art for improved redox flow batterychemistries and systems.

It is the object of the present invention to comply with the aboveneeds.

Although the present invention is described in detail below, it is to beunderstood that this invention is not limited to the particularmethodologies, protocols and reagents described herein as these mayvary. It is also to be understood that the terminology used herein isnot intended to limit the scope of the present invention which will belimited only by the appended claims. Unless defined otherwise, alltechnical and scientific terms used herein have the same meanings ascommonly understood by one of ordinary skill in the art.

In the following, the features of the present invention will bedescribed. These features are described for specific embodiments. Itshould, however, be understood that they may be combined in any mannerand in any number to generate additional embodiments. The variouslydescribed examples and preferred embodiments should not be construed tolimit the present invention to only explicitly described embodiments.This present description should be understood to support and encompassembodiments, which combine the explicitly described embodiments with anynumber of the disclosed and/or preferred features. Furthermore, anypermutations and combinations of all described features in thisapplication shall be considered supported by the description of thepresent application, unless it is understood otherwise.

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the term “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated member, integer or step but not the exclusion of any othernon-stated member, integer or step. The term “consist of” is aparticular embodiment of the term “comprise”, wherein any othernon-stated member, integer or step is excluded. In the context of thepresent invention, the term “comprise” encompasses the term “consistof”. The term “comprising” thus encompasses “including” as well as“consisting” e.g., a composition “comprising” X may consist exclusivelyof X or may include something additional e.g., X+Y.

The terms “a” and “an” and “the” and similar reference used in thecontext of describing the invention (especially in the context of theclaims) are to be construed to cover both the singular and the plural,unless otherwise indicated herein or clearly contradicted by context.Recitation of ranges of values herein is merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range. Unless otherwise indicated herein, eachindividual value is incorporated into the specification as if it wereindividually recited herein. No language in the specification should beconstrued as indicating any non-claimed element essential to thepractice of the invention.

The word “substantially” does not exclude “completely” e.g., acomposition which is “substantially free” from Y may be completely freefrom Y. Where necessary, the word “substantially” may be omitted fromthe definition of the invention.

The term “about” in relation to a numerical value x means x±10%.

For the purposes of this invention, the term “quinone” includes acompound having one or more conjugated, C₃₋₁₀ carbocyclic, fused rings,substituted, in oxidized form, with two or more oxo groups, which are inconjugation with the one or more conjugated rings. Preferably, thenumber of rings is from one to ten, e.g., one, two, or three, and eachring has 6 members.

The present invention provides novel compounds, compositions comprisingthe same and their unprecedented use in various applications, inter aliaas as redox active species in redox flow batteries. Means and methodsfor preparing said compounds and compositions are also provided. Theinventive compounds may advantageously be obtained from lignin, crudeoil, coal or pure organic substances. In particular, lignin derivativesproduced as waste or by-products of the pulping industry have previouslylargely been unexploited and can be valorized by the methods of thepresent invention. Specifically, the present inventors developed a novelprocess for obtaining valuable lignin-derived low molecular weightprecursor compounds (in particular aromatic compounds, preferablyquinones and hydroquinones) that are subjected to a sulfonationreaction. Without wishing to be bound by theory, it is envisaged thatthe introduction of sulfonyl groups into the molecular (aromatic)skeleton improves solubility and electrochemical properties of theresulting compounds. The resulting sulfonated low molecular weight(“lmw”) preferably aromatic target compounds are thus useful in variousapplications, inter alia as electrolytes for redox flow batteryapplications. Advantageously, the inventors further discovered thatcompositions comprising or (essentially) consisting of mixtures ofsulfonated target compounds as defined herein exhibit (in particularelectrochemical) properties that are comparable to those of the puretarget compounds. In consequence, the invention provides mixtures ofsulfonated target compounds that are directly obtainable from lignin (orcrude oil, coal, pure organic substances) processing as “ready-to-use”products, and in particular as electrolytes (or slurry, solids) in redoxflow batteries. The invention thus surprisingly opens up unprecedentedpossibilities to obtain effective redox flow battery electrolytes atlarge scale and low cost by exploiting mass by-products of the pulpingindustry (or other feedstock materials).

The sulfonated lmw (aromatic) target compounds described herein areobtainable by a method comprising the steps of (1) providing a startingmaterial; (2) optionally subjecting said starting material to a processsuitable to obtain at least one low molecular weight precursor compound;(3) isolating and optionally modifying at least one low molecular weightprecursor compound; thereby obtaining at least one (optionally modified)low molecular weight aromatic precursor compound; (4) subjecting said atleast one (optionally modified) low molecular weight precursor compoundto a sulfonation reaction, wherein one or more —SO₃H groups areintroduced into said at least one precursor compound; thereby obtainingat least one sulfonated low molecular weight aromatic compound or acomposition comprising the same or (essentially) consisting thereof;wherein said starting material is preferably selected fromlignocellulosic material, crude oil, coal or pure organic substances.

Advantageously, the present invention inter alia allows for thevalorization of lignocellulosic material, which is currently discardedas waste material of the pulping industry. According to the presentinvention, sulfonated lmw (aromatic) target compounds may be obtainedfrom lignin by a method combining two separate processes, i.e. by usingby-products of the pulping process as starting material for subsequentgeneration of sulfonated lmw (aromatic) lignin-derived compounds andcompositions comprising the same. That approach preferably has theadvantage of reducing energy consumption and employing renewableresources. The inventive method may advantageously be employed toprovide (ideally within an integrated plant) lignin-derived lmw(aromatic) compounds and compositions comprising the same. Thesecompounds and compositions serve as precursors for the production ofsulfonated lmw (aromatic) lignin-derived compounds and compositionscomprising the same that can be used as redox active compounds in redoxflow batteries, which were previously (economically) amenable bynon-renewable sources only, or can be employed in various otherapplication.

Accordingly, in a first aspect, the present invention relates to novelsulfonated lmw (aromatic) compounds and composition comprising or(essentially) consisting of the same. In a further aspect, the inventionprovides methods for preparing said compounds and compositions. Saidmethods preferably comprise the general method steps (1)-(4) asindicated above. In a particular aspect, the present invention featuresa method for preparing sulfonated lmw (aromatic) compounds (andcompositions) from lignin. The inventive methods preferably furtherentail method steps (1)-(5) and optionally (6), (7) and/or (8) asdescribed in more detail below.

Redox Active Compounds and Compositions

The inventive method provides sulfonated (optionally lignin-derived)target compounds (and compositions comprising or (essentially)consisting of the same), which are preferably redox active. Preferably,the term “redox active” refers to the capability of a compound (or acomposition comprising the same) to participate in a redox reaction.Such redox active compounds typically have energetically accessiblelevels that allow redox reactions to alter their charge state (wherebyelectrons are either removed (oxidation—yielding an oxidized form of thecompound) from atoms of the compound being oxidized or transferred tothe compound being reduced (reduction—yielding a reduced from of thecompound)). A “redox active” compound may thus be understood as achemical compound, which may form a pair of an oxidizing and reducingagent, i.e. a redox pair.

The inventive method preferably provides redox active compounds andcompositions comprising or (essentially) consisting of the same, morepreferably lignin-derived compounds (or compositions) that areparticularly envisaged as redox flow battery electrolytes. Saidcompounds (or compositions) are also referred to as “target compounds”or “target compositions” herein and may preferably be obtained fromlignin (or alternatively from crude oil, coal or pure organicsubstances) by applying the methods disclosed herein. Preferred(optionally lignin-derived) target compounds in accordance with theinvention are sulfonated low molecular weight organic, preferablyaromatic, target compounds, in particular sulfonated (hydro-)quinones.

Lignin-derived compositions according to the invention preferablycomprise or (essentially) consist of at least one sulfonated (optionallylignin-derived) lmw organic compound as defined herein, which ispreferably an aromatic compound. It will be understood that the term“composition” encompasses compositions comprising or (essentially)consisting of 2, or more, preferably 3 or more different sulfonatedtarget compounds. By “essentially consisting of” is meant a compositioncomprising one or more sulfonated target compounds, with a minor amountof by-products, impurities or contaminants only (which are notsulfonated target compounds as defined herein), wherein said by-productsor impurities constitute preferably less than 10%, preferably less than5% the overall composition by dry content mass. By “consisting of” ismeant a composition that is exclusively composed of at least twosulfonated target compounds, and does not comprise any impurities orby-products as defined above. Accordingly, the present invention interalia encompasses the use of a (optionally lignin-derived) compositionexclusively consisting of two or more different sulfonated targetcompound as defined herein. In other words, sulfonated target compounds(which may be used as redox flow battery electrolytes in the form of acomposition) may exhibit a purity of 100%. It is thus envisaged that thelignin-derived composition comprises or (essentially) consists ofmixtures of sulfonated lmw (aromatic) (optionally lignin-derived)compounds as defined herein.

Preferred sulfonated lmw (aromatic) (optionally lignin-derived)compounds according to the present invention are represented by thefollowing structural formulae (X), (XI), (XII), (XIII), (XIV) or (XV)depicted below:

-   -   wherein each R¹, R², R³ or R⁴ is independently selected from        hydrogen, hydroxy, carboxy, linear or branched, optionally        substituted, C₁₋₆ alkyl, linear or branched, optionally        substituted, C₁₋₆ alkenyl, linear or branched, optionally        substituted, C₁₋₆ alcohol, linear or branched, optionally        substituted, C₁₋₆ aminoalkyl, linear or branched, optionally        substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally        substituted, C₁₋₆ alkoxy, linear or branched, optionally        substituted, C₁₋₆ aldehyde, ester, halogen, amine, amino, amide,        nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and        sulfonyl,    -   provided that at least one of R¹-R⁴ is SO₃H;

-   -   wherein each R¹, R², R³, R⁴, R⁵ or R⁶ is independently selected        from hydrogen, hydroxy, carboxy, linear or branched, optionally        substituted, C₁₋₆ alkyl, linear or branched, optionally        substituted, C₁₋₆ alkenyl, linear or branched, optionally        substituted, C₁₋₆ alcohol, linear or branched, optionally        substituted, C₁₋₆ aminoalkyl, linear or branched, optionally        substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally        substituted, C₁₋₆ alkoxy, linear or branched, optionally        substituted, C₁₋₆ aldehyde, ester, halogen, amine, amino, amide,        nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and        sulfonyl,    -   provided that at least one of R¹-R⁶ is SO₃H;

-   -   wherein each R¹, R², R³, R⁴, R⁵, R⁶, R⁷ or R⁸ is independently        selected from hydrogen, hydroxy, carboxy, linear or branched,        optionally substituted, C₁₋₆ alkyl, linear or branched,        optionally substituted, C₁₋₆ alkenyl, linear or branched,        optionally substituted, C₁₋₆ alcohol, linear or branched,        optionally substituted, C₁₋₆ aminoalkyl, linear or branched,        optionally substituted, C₁₋₆ carboxyalkyl, linear or branched,        optionally substituted, C₁₋₆ alkoxy, linear or branched,        optionally substituted, C₁₋₆ aldehyde, ester, halogen, amine,        amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl,        cyanide and sulfonyl, provided that at least one of R¹-R⁸ is        SO₃H,    -   preferably selected from a sulfonated compound according to        Table 1, 2 or 3.

Alternatively, preferred sulfonated lmw (aromatic) (optionallylignin-derived) compounds according to the present invention may berepresented by the following structural formulae (X), (XI), (XII),(XIII), (XIV) or (XV) depicted below:

-   -   wherein each R¹, R², R³ or R⁴ is independently selected from        hydrogen (H), hydroxy (OH), carboxy (COOH), optionally        substituted C₁₋₆ alkyl (including C_(n)H_(2n)OH and        C_(n)H_(2n)NH₂ wherein n is 1-6), carboxylic acids, esters,        halogen, optionally substituted C₁₋₆ alkoxy (including methoxy,        ethoxy), optionally substituted amino (including primary,        secondary, tertiary and quaternary amines), amide, nitro,        carbonyl, phosphoryl, phosphonyl, cyanide or sulfonyl (SO₃H);    -   provided that at least one of R¹-R⁴ is SO₃H;

-   -   wherein each R¹, R², R³, R⁴, R⁵ or R⁶ is independently selected        from hydrogen (H), hydroxy (OH), carboxy (COOH), optionally        substituted C₁₋₆ alkyl (including C_(n)H_(2n)OH and        C_(n)H_(2n)NH₂ wherein n is 1-6), carboxylic acids, esters,        halogen, optionally substituted C₁₋₆ alkoxy (including methoxy,        ethoxy), optionally substituted amino (including primary,        secondary, tertiary and quaternary amines), amide, nitro,        carboxyl, phosphoryl, phosphonyl, cyanide or sulfonyl (SO₃H);    -   provided that at least one of R¹-R⁶ is SO₃H;

-   -   wherein each R¹, R², R³, R⁴, R⁵, R⁶, R⁷ or R⁸ is independently        selected from hydrogen (H), hydroxy (OH), carboxy (COOH),        optionally substituted C₁₋₆ alkyl (including C_(n)H_(2n)OH and        —C_(n)H_(2n)NH₂ wherein n is 1-6), carboxylic acids, esters,        halogen, optionally substituted C₁₋₆ alkoxy (including methoxy,        ethoxy), optionally substituted amino (including primary,        secondary, tertiary and quaternary amines), amide, nitro,        carboxyl, phosphoryl, phosphonyl, cyanide or sulfonyl (SO₃H);        provided that at least one of R¹-R⁸ is SO₃H.

Preferably in compounds characterized by Formula (X) or (XI), 1 to 3,more preferably 2 of R¹ to R⁴ are SO₃H. Preferably, in compoundscharacterized by Formula (XII) or (XIII), 1 to 4, more preferably 2 ofR¹ to R⁶ are SO₃H. Preferably, in compounds characterized by Formula(XIV) or (XV), 1 to 5, more preferably 2 of R¹ to R⁸ are SO₃H.

The invention further provides a composition comprising at least twosulfonated low molecular weight aromatic compounds as described herein,preferably at least two distinct low molecular weight aromatic compoundswith at least one compound being in the oxidized state according toFormula (X), (XII) or (XIV), and/or at least corresponding compoundbeing in the reduced state according to Formula (XI), (XIII) or (XV).

In said composition, the said at least two sulfonated low molecularweight aromatic compounds are characterized by the following:

(a) at least one compound according to Formula (X) and (XI), preferablyas defined in claim 2 or 3, preferably at least one compound of Formula(X) (oxidized state) and at least one corresponding compound of Formula(XI) (reduced state);

(b) at least one compound according to Formula (XII) and (XIII),preferably as defined herein, preferably at least one compound ofFormula (XII) (oxidized state) and at least one corresponding compoundof Formula (XIII) (reduced state); and/or

(c) at least one compound according to Formula (XIV) and (XV),optionally as defined herein, preferably at least one compound ofFormula (XIV) (oxidized state) and at least one corresponding compoundof Formula (XV) (reduced state).

Said composition may in particular comprise:

(a) at least two compounds according to Formula (X) and (XI), whereinsaid at least two compounds are distinctly sulfonated and/orsubstituted, preferably at least two distinct compounds being in theoxidized state according to Formula (X) and at least two correspondingdistinct compounds according to Formula (XI) in the respective reducedstate;

(b) at least two compounds according to Formula (XII) or (XIII), whereinsaid at least two compounds are distinctly sulfonated and/orsubstituted, preferably at least two distinct compounds being in theoxidized state according to Formula (XII) and at least two correspondingdistinct compounds according to Formula (XIII) in the respective reducedstate; and/or

(c) at least two compounds according to Formula (XIV) or (XV), whereinsaid at least two compounds are distinctly sulfonated and/orsubstituted, preferably at least two distinct compounds being in theoxidized state according to Formula (XIV) and at least two correspondingdistinct compounds according to Formula (XV) in the respective reducedstate.

It is therefore inter alia envisaged herein that the inventivecomposition may comprise (optionally distinctly sulfonated and/orsubstituted) benzohydroquinones (according to Formula (XI)), (optionallydistinctly sulfonated and/or substituted) napththohydroquinones(according to Formula (XIII)), and/or (optionally distinctly sulfonatedand/or substituted) anthrahydroquinones (according to Formula (XV)). Itis inter alia also envisaged that the inventive composition may comprise(optionally distinctly sulfonated and/or substituted) benzoquinones(according to Formula (X)), (optionally distinctly sulfonated and/orsubstituted) napththoquinones (according to Formula (XII)), and/or(optionally distinctly sulfonated and/or substituted)anthrahydroquinones (according to Formula (XIV)). Mixtures of theaforementioned quinones and hydroquinones are also envisaged for theinventive compositions.

Each of said at least two compounds may comprise at least two SO₃Hgroups, preferably two SO₃H groups.

The lignin-derived composition according to the present invention maythus comprise or (essentially) consist of sulfonated lmw (aromatic)(optionally lignin-derived) compounds represented by structural formula(X), (XI), (XII), (XIII), (XIV) or (XV) as defined above, or mixturesthereof, in particular mixtures of sulfonated lmw (aromatic) (optionallylignin-derived) compounds represented by structural formulae (X) and/or(XI) (each one or both optionally exhibiting a distinct substitutionpattern), mixtures of sulfonated lmw (aromatic) lignin-derived compoundsrepresented by structural formulae (XII) and/or (XIII) (each one or bothoptionally exhibiting a distinct substitution pattern), or mixtures ofsulfonated lmw (aromatic) lignin-derived compounds represented bystructural formulae (XIV) and/or (XV) (each one or both optionallyexhibiting a distinct substitution pattern).

In this context, the term “mixture” refers to a plurality of “different”sulfonated lmw (aromatic) lignin-derived compounds. Said compoundscomprised by the mixture may be different (a) by virtue of their basicstructure formulae (i.e. the term comprises for instance mixtures ofcompounds according to structural formulae (X), (XI) and (XII) or (b) byvirtue of their substitution pattern, while optionally sharing the samebasic structural formulae (i.e. the term comprises for instance mixturesof compounds according to structural formula (X) exhibiting differentsubstitution patterns), or combinations thereof. By the term“substitution pattern” or “derivatization pattern” is meant the number,type and distribution of substituents, provided that all “different”compounds present in the mixture fall under the respective definitionsgiven above.

Specifically, sulfonated lmw aromatic (optionally lignin-derived)compounds in accordance with the present invention may be characterizedby Formula (X) or (XI) wherein R¹ and R⁴ are independently selected fromH or SO₃H, R² is selected from H, OH, or C₁-C₆ alkoxy, preferablymethoxy, or SO₃H, R³ is selected from H, OH or C₁-C₆ alkoxy, preferablymethoxy. In some preferred compounds, R¹ and R⁴ are SO₃H, or R¹ and R³may be SO₃H. Compositions comprising or (essentially) consisting ofmixtures of any of the aforementioned compounds are also envisaged.

Further preferred compounds characterized by Formula (X) or (XI) mayexhibit the following substitution pattern:

a) R⁴ is SO₃H;

b) R⁴ is SO₃H, R³ is methoxy;

c) R⁴ is SO₃H, R² and R³ are methoxy;

d) R¹ and R⁴ are SO₃H;

e) R¹ and R⁴ are SO₃H, R³ is methoxy;

f) R¹ and R⁴ are SO₃H, R² and R³ are methoxy;

g) R² and R⁴ are SO₃H, and R³ is methoxy, wherein each of the others ofR¹-R⁴ may be H (unless it is defined otherwise according to a)-g)).

Compositions comprising or (essentially) consisting of mixtures ofcompounds according to a)-g) are also envisaged.

Further, sulfonated lmw aromatic (optionally lignin-derived) compoundsin accordance with the present invention may be characterized by Formula(XII) or (XIII), wherein R¹ and R² are independently selected from H, OHor C₁-C₆ alkoxy, preferably methoxy, R³-R⁶ are independently selectedfrom H or SO₃H. In preferred compounds, R¹ and R⁴ or R¹ and R⁵ or R³ andR⁵ may be SO₃H. Compositions comprising or (essentially) consisting ofmixtures of any of the aforementioned compounds are also envisaged.

Further, sulfonated lmw aromatic (optionally lignin-derived) compoundsin accordance with the present invention may be characterized by Formula(XIV) or (XV), wherein R¹, R² and R⁴ are independently selected from H,OH or C₁-C₆ alkoxy, preferably methoxy, and R³, R⁵-R⁸ are independentlyselected from H oder SO₃H. In some preferred compounds, R² and R⁶ or R²and R⁷ or R¹ and R⁵ may be SO₃H.

Further preferred compounds characterized by Formula (XIV) or (XV)exhibit the following substitution pattern:

a) R¹ is SO₃H;

b) R² is SO₃H; R¹, R³ and R⁴ are optionally OH;

c) R⁶ is SO₃H; R¹ and R⁴ or R¹, R² and R⁴ are optionally OH;

d) R² and R⁶ are SO₃H; R¹ and R⁴ or R¹, R³ and R⁴ are optionally OH;

e) R³ and R⁶ are SO₃H; R¹, R² and R⁴ are optionally OH;

f) R² and R⁷ are SO₃H;

g) R¹ and R⁴ are SO₃H;

wherein each of the remaining R¹-R⁸ may be H (unless it is SO₃H or OH).

Compositions comprising or (essentially) consisting of mixtures ofcompounds according to a)-g) are also envisaged.

Preferred (optionally lignin-derived) sulfonated target compoundsaccording to the present invention comprise1,4-benzoquinone-2,5-disulfonic acid, 1,4-benzoquinone-2,6-disulfonicacid, 1,4-benzoquinone-2-sulfonic acid,1,4-naphthoquinone-2,6-disulfonic acid,1,4-naphthoquinone-2,7-disulfonic acid,1,4-naphthoquinone-5,7-disulfonic acid, 1,4-naphthoquinone-5-sulfonicacid, 1,4-naphthoquinone-2-sulfonic acid,9,10-anthraquinone-2,6-disulfonic acid,9,10-anthraquinone-2,7-disulfonic acid,9,10-anthraquinone-1,5-disulfonic acid, 9,10-anthraquinone-1-sulfonicacid, 9,10-anthraquinone-2-sulfonic acid, or derivatives thereof.Compositions comprising or (essentially) consisting of mixtures of saidcompounds (preferably comprising either benzoquinones or naphthoquinonesor anthraquinones each with different derivatization patterns) are alsoenvisaged herein.

Preferred compounds according to the invention are characterized byFormula (X) or (XI) and may exhibit a derivatization pattern asindicated in table 1 below.

TABLE 1 Preferred structures for Benzoquinone and benzohydroquinonederivatives:

C1-C6-alkoxy SO₃H substituents OH substituents substituted Alkylsubstituents ID position amount position amount position amount positionamount  1 R¹ Mono- — None — None — None  2 R¹-R⁴ Di- — None — None —None  3 R¹-R⁴ Tri- — None — None — None  4 R¹ Mono- — None R²-R⁴ Mono- —None  5 R¹ Mono- — None — None R²-R⁴ Mono-  6 R¹ Mono- — None R²-R⁴Mono- R²-R⁴ Mono-  7 R¹ Mono- — None R²-R³ Di- — None  8 R¹ Mono- — None— None R²-R⁴ Di-  9 R¹ Mono- — None R²-R³ Di- R²-R⁴ Mono- 10 R¹ Mono- —None R²-R⁴ Mono- R²-R⁴ Di- 11 R¹-R⁴ Di- — None R²-R⁴ Mono- — None 12R¹-R⁴ Di- — None — None R²-R⁴ Mono- 13 R¹-R⁴ Di- — None R²-R³ Di- — None14 R¹-R⁴ Di- — None — None R²-R⁴ Di- 15 R¹-R⁴ Tri- — None R²-R⁴ Mono- —None 16 R¹-R⁴ Tri- — None — None R²-R⁴ Mono-

Particularly preferred benzoquinone and benzohydroquinone derivativesare molecules with ID No. 1-3 and 11-16.

Preferred compounds according to the invention are characterized byFormula (XII) or (XIII) and may exhibit a derivatization pattern asindicated in table 2 below.

TABLE 2 Preferred structures for Napthoquinone and Naphthohydroquinonederivatives:

C1-C6-alkoxy SO₃H substituents OH substituents substituted Alkylsubstituents ID position amount position amount position amount positionamount 17 R¹, R³, R⁴ Mono- — None — None — None 18 R¹-R⁶ Di- — None —None — None 19 R¹-R⁶ Tri- — None — None — None 20 R¹-R⁶ Tetra- — None —None — None 21 R¹-R⁶ Penta- — None — None — None 22 R¹, R³, R⁴ Mono- —None R¹-R⁶ Mono- — None 23 R¹, R³, R⁴ Mono- — None — None R¹-R⁶ Mono- 24R¹, R³, R⁴ Mono- — None R¹-R⁶ Mono- R¹-R⁶ Mono- 25 R¹, R³, R⁴ Mono- R³,R⁶ Di- — None — None 26 R¹, R³, R⁴ Mono- — None R¹-R⁶ Di- — None 27 R¹,R³, R⁴ Mono- — None — None R1-R⁶ Di- 28 R¹, R³, R⁴ Mono- R³, R⁶ Di-R¹⁻²-R⁴⁻⁵ Mono- — None 35 R¹, R³, R⁴ Mono- R³, R⁶ Di- — None R¹⁻²-R⁴⁻⁵Mono- 36 R¹, R³, R⁴ Mono- R³, R⁶ Di- R¹⁻²-R⁴⁻⁵ Mono- R¹⁻²-R⁴⁻⁵ Mono- 37R¹, R³, R⁴ Mono- R³, R⁶ Di- R¹⁻²-R⁴⁻⁵ Di- — None 38 R¹, R³, R⁴ Mono- R³,R⁶ Di- — None R¹⁻²-R⁴⁻⁵ Di- 39 R¹, R³, R⁴ Mono- R³, R⁶ Di- R¹⁻²-R⁴⁻⁵ Di-R¹⁻²-R⁴⁻⁵ Mono- 40 R¹, R³, R⁴ Mono- R³, R⁶ Di- R¹⁻²-R⁴⁻⁵ Mono- R¹⁻²-R⁴⁻⁵Di- 35 R¹, R³, R⁴ Mono- — None R1-R⁶ Di- R¹-R⁶ Mono- 36 R¹, R³, R⁴ Mono-— None R¹-R⁶ Mono- R1-R⁶ Di- 37 R¹, R³, R⁴ Mono- — None R1-R⁶ Di- R1-R⁶Di- 38 R¹, R³, R⁴ Mono- — None R1-R⁶ Tri- — None 39 R¹, R³, R⁴ Mono- —None — None R1-R⁶ Tri- 40 R¹, R³, R⁴ Mono- — None R1-R⁶ Tri- R¹-R⁶ Mono-41 R¹, R³, R⁴ Mono- — None R¹-R⁶ Mono- R1-R⁶ Tri- 42 R¹, R³, R⁴ Mono- —None R1-R⁶ Tri- R¹-R⁶ Di- 43 R¹, R³, R⁴ Mono- — None R¹-R⁶ Di- R1-R⁶Tri- 44 R¹, R³, R⁴ Mono- — None R1-R⁶ Tetra- — None 45 R¹, R³, R⁴ Mono-— None — None R1-R⁶ Tera- 46 R¹, R³, R⁴ Mono- — None R1-R⁶ Tetra- R¹-R⁶Mono- 47 R¹, R³, R⁴ Mono- — None R¹-R⁶ Mono- Rl-R⁶ Tetra- 48 R¹-R⁶ Di- —None R¹-R⁶ Mono- — None 49 R¹-R⁶ Di- — None — None R¹-R⁶ Mono- 50 R¹-R⁶Di- — None R¹-R⁶ Mono- R¹-R⁶ Mono- 51 R¹-R⁶ Di- R³, R⁶ Di- — None — None52 R¹-R⁶ Di- — None R1-R⁶ Di- — None 53 R¹-R⁶ Di- — None — None R1-R⁶Di- 54 R¹-R⁶ Di- R³, R⁶ Di- R¹⁻²-R⁴⁻⁵ Mono- — None 55 R¹-R⁶ Di- R³, R⁶Di- — None R¹⁻²-R⁴⁻⁵ Mono- 56 R¹-R⁶ Di- R³, R⁶ Di- R¹⁻²-R⁴⁻⁵ Mono-R¹⁻²-R⁴⁻⁵ Mono- 57 R¹-R⁶ Di- R³, R⁶ Di- R¹⁻²-R⁴⁻⁵ Di- — None 58 R¹-R⁶Di- R³, R⁶ Di- — None R¹⁻²-R⁴⁻⁵ Di- 59 R¹-R⁶ Di- — None R1-R⁶ Di- R¹-R⁶Mono- 60 R¹-R⁶ Di- — None R¹-R⁶ Mono- R1-R⁶ Di- 61 R¹-R⁶ Di- — NoneR1-R⁶ Di- R1-R⁶ Di- 62 R¹-R⁶ Di- — None R1-R⁶ Tri- — None 63 R¹-R⁶ Di- —None — None R1-R⁶ Tri- 64 R¹-R⁶ Di- — None R1-R⁶ Tri- R¹-R⁶ Mono- 65R¹-R⁶ Di- — None R¹-R⁶ Mono- R1-R⁶ Tri- 66 R¹-R⁶ Tri- — None R¹-R⁶ Mono-— None 67 R¹-R⁶ Tri- — None — None R¹-R⁶ Mono- 68 R¹-R⁶ Tri- — NoneR¹-R⁶ Mono- R¹-R⁶ Mono- 69 R¹-R⁶ Tri- R³, R⁶ Di- — None — None 70 R¹-R⁶Tri- — None R1-R⁶ Di- — None 71 R¹-R⁶ Tri- — None — None R1-R⁶ Di- 72R¹-R⁶ Tri- R³, R⁶ Di- R¹⁻²-R⁴⁻⁵ Mono- — None 73 R¹-R⁶ Tri- R³, R⁶ Di- —None R¹⁻²-R⁴⁻⁵ Mono- 74 R¹-R⁶ Tri- — None R1-R⁶ Di- R¹-R⁶ Mono- 75 R¹-R⁶Tri- — None R¹-R⁶ Mono- R1-R⁶ Di- 76 R¹-R⁶ Tri- — None R1-R⁶ Tri- — None77 R¹-R⁶ Tri- — None — None R1-R⁶ Tri- 78 R¹-R⁶ Tetra- — None R¹-R⁶Mono- — None 79 R¹-R⁶ Tetra- — None — None R¹-R⁶ Mono- 80 R¹-R⁶ Tetra- —None R¹-R⁶ Mono- R¹-R⁶ Mono- 81 R¹-R⁶ Tetra- R³, R⁶ Di- — None — None 82R¹-R⁶ Tetra- — None R1-R⁶ Di- — None 83 R¹-R⁶ Tetra- — None — None R1-R⁶Di- 84 R¹-R⁶ Penta- — None R¹-R⁶ Mono- — None 85 R¹-R⁶ Penta- — None —None R¹-R⁶ Mono-

Particularly preferred naphthoquinone and naphthohydroquinonederivatives are molecules with ID No. 17-19, 22-23, 48-49, 52-53, 59-61,66-68, 70-71, 74-75.

Preferred compounds according to the invention are characterized byFormula (XIV) or (XV) and may exhibit a derivatization pattern asindicated in table 3 below.

TABLE 3 Preferred structures for Anthraquinone and AnthrahydroquinoneDerivatives:

C1-C6-alkoxy SO₃H substituents OH substituents substituted Alkylsubstituents ID position amount position amount position amount positionamount  86 R¹⁻² Mono- — None — None — None  87 R¹-R⁸ Di- — None — None —None  88 R¹-R⁸ Tri- — None — None — None  89 R¹-R⁸ Tetra- — None — None— None  90 R¹-R⁸ Penta- — None — None — None  91 R¹⁻² Mono- R¹-R⁸ Mono-— None — None  92 R¹⁻² Mono- — None R¹-R⁸ Mono- — None  93 R¹⁻² Mono- —None — None R¹-R⁸ Mono-  94 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Mono- — None 95 R¹⁻² Mono- R¹-R⁸ Mono- — None R¹-R⁸ Mono-  96 R¹⁻² Mono- — NoneR¹-R⁸ Mono- R¹-R⁸ Mono-  97 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Mono- R¹-R⁸Mono-  98 R¹⁻² Mono- R¹⁻⁸ Di- — None — None  99 R¹⁻² Mono- — None R¹-R⁸Di- — None 100 R¹⁻² Mono- — None — None R¹-R⁸ Di- 101 R¹⁻² Mono- R¹-R⁸Di- R¹-R⁸ Mono- — None 102 R¹⁻² Mono- R¹-R⁸ Di- — None R¹-R⁸ Mono- 103R¹⁻² Mono- R³, R⁶ Di- R¹-R⁸ Mono- R¹-R⁸ Mono- 104 R¹⁻² Mono- R¹-R⁸ Mono-R¹-R⁸ Di- — None 105 R¹⁻² Mono- — None R¹-R⁸ Di- R¹-R⁸ Mono- 106 R¹⁻²Mono- R¹-R⁸ Mono- R¹-R⁸ Di- R¹-R⁸ Mono- 107 R¹⁻² Mono- R¹-R⁸ Mono- —None R¹-R⁸ Di- 108 R¹⁻² Mono- — None R¹-R⁸ Mono- R¹-R⁸ Di- 109 R¹⁻²Mono- R¹-R⁸ Mono- R¹-R⁸ Mono- R¹-R⁸ Di- 110 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸Di- — None 111 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸ Di- R¹-R⁸ Mono- 112 R¹⁻² Mono-R¹-R⁸ Di- — None R¹-R⁸ Di- 113 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸ Mono- R¹-R⁸Di- 114 R¹⁻² Mono- — None R¹-R⁸ Di- R¹-R⁸ Di- 115 R¹⁻² Mono- R¹-R⁸ Mono-R¹-R⁸ Di- R¹-R⁸ Di- 116 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸ Di- R¹-R⁸ Di- 117R¹⁻² Mono- R¹⁻⁸ Tri- — None — None 118 R¹⁻² Mono- — None R¹-R⁸ Tri —None 119 R¹⁻² Mono- — None — None R¹-R⁸ Tri 120 R¹⁻² Mono- R¹-R⁸ Tri-R¹-R⁸ Mono- — None 121 R¹⁻² Mono- R¹-R⁸ Tri- — None R¹-R⁸ Mono- 122 R¹⁻²Mono- R³, R⁶ Tri- R¹-R⁸ Mono- R¹-R⁸ Mono- 123 R¹⁻² Mono- R¹-R⁸ Tri-R¹-R⁸ Di- — None 124 R¹⁻² Mono- R¹-R⁸ Tri- — None R¹-R⁸ Di- 125 R¹⁻²Mono- R¹-R⁸ Tri- R¹-R⁸ Di- R¹-R⁸ Mono- 126 R¹⁻² Mono- R¹-R⁸ Tri- R¹-R⁸Mono- R¹-R⁸ Di- 127 R¹⁻² Mono- R³, R⁶ Tri- R¹-R⁸ Di- R¹-R⁸ Di- 128 R¹⁻²Mono- R¹-R⁸ Tri- R¹-R⁸ Tri- — None 129 R¹⁻² Mono- R¹-R⁸ Tri- — NoneR¹-R⁸ Tri- 130 R¹⁻² Mono- R¹-R⁸ Tri- R¹-R⁸ Tri- R¹-R⁸ Mono- 131 R¹⁻²Mono- R³, R⁶ Tri- R¹-R⁸ Mono- R¹-R⁸ Tri- 132 R¹⁻² Mono- R¹-R⁸ Mono-R¹-R⁸ Tri- — None 133 R¹⁻² Mono- — None R¹-R⁸ Tri- R¹-R⁸ Mono- 134 R¹⁻²Mono- R¹-R⁸ Mono- R³, R⁶ Tri- R¹-R⁸ Mono- 135 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸Tri- — None 136 R¹⁻² Mono- — None R¹-R⁸ Tri- R¹-R⁸ Di- 137 R¹⁻² Mono-R¹-R⁸ Di- R¹-R⁸ Tri- R¹-R⁸ Mono- 138 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Tri-R¹-R⁸ Di- 139 R¹⁻² Mono- R¹-R⁸ Di- R³, R⁶ Tri- R¹-R⁸ Di- 140 R¹⁻² Mono-— None R¹-R⁸ Tri- R¹-R⁸ Tri- 141 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Tri- R¹-R⁸Tri- 142 R¹⁻² Mono- R¹-R⁸ Mono- — None R¹-R⁸ Tri- 143 R¹⁻² Mono- — NoneR¹-R⁸ Mono- R¹-R⁸ Tri- 144 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Mono- R³, R⁶Tri- 145 R¹⁻² Mono- R¹-R⁸ Di- — None R¹-R⁸ Tri- 146 R¹⁻² Mono- — NoneR¹-R⁸ Di- R¹-R⁸ Tri- 147 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Tri- 148R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Di- R¹-R⁸ Tri- 149 R¹⁻² Mono- R¹-R⁸ Di-R¹-R⁸ Di- R³, R⁶ Tri- 150 R¹⁻² Mono- R¹⁻⁸ Quart- — None — None 151 R¹⁻²Mono- — None R¹-R⁸ Quart- — None 152 R¹⁻² Mono- — None — None R1-R⁸Quart- 153 R¹⁻² Mono- R¹-R⁸ Quart- R¹-R⁸ Mono- — None 154 R¹⁻² Mono-R¹-R⁸ Quart- — None R¹-R⁸ Mono- 155 R¹⁻² Mono- R³, R⁶ Quart- R¹-R⁸ Mono-R¹-R⁸ Mono- 156 R¹⁻² Mono- R¹-R⁸ Quart- R¹-R⁸ Di- — None 157 R¹⁻² Mono-R¹-R⁸ Quart- — None R¹-R⁸ Di- 158 R¹⁻² Mono- R¹-R⁸ Quart- R¹-R⁸ Di-R¹-R⁸ Mono- 159 R¹⁻² Mono- R¹-R⁸ Quart- R¹-R⁸ Mono- R¹-R⁸ Di- 160 R¹⁻²Mono- R¹-R⁸ Quart- R¹-R⁸ Tri- — None 161 R¹⁻² Mono- R¹-R⁸ Quart- — NoneR¹-R⁸ Tri- 162 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Quart- — None 163 R¹⁻² Mono-— None R¹-R⁸ Quart- R¹-R⁸ Mono- 164 R¹⁻² Mono- R¹-R⁸ Mono- R³, R⁶ Quart-R¹-R⁸ Mono- 165 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸ Quart- — None 166 R¹⁻² Mono-— None R¹-R⁸ Quart- R¹-R⁸ Di- 167 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸ Quart-R¹-R⁸ Mono- 168 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Quart- R¹-R⁸ Di- 169 R¹⁻²Mono- — None R¹-R⁸ Quart- R¹-R⁸ Tri- 170 R¹⁻² Mono- R¹-R⁸ Tri R¹-R⁸Quart- — None 171 R¹⁻² Mono- R¹-R⁸ Mono- — None R¹-R⁸ Quart- 172 R¹⁻²Mono- — None R¹-R⁸ Mono- R¹-R⁸ Quart- 173 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸Mono- R³, R⁶ Quart- 174 R¹⁻² Mono- R¹-R⁸ Di- — None R¹-R⁸ Quart- 175R¹⁻² Mono- — None R¹-R⁸ Di- R¹-R⁸ Quart- 176 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸Mono- R¹-R⁸ Quart- 177 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Di- R¹-R⁸ Quart- 178R¹⁻² Mono- R¹-R⁸ Tri- — None R¹-R⁸ Quart- 179 R¹⁻² Mono- — None R¹-R⁸Tri- R¹-R⁸ Quart- 180 R¹⁻² Mono- R¹⁻⁸ Pent- — None — None 181 R¹⁻² Mono-— None R¹-R⁸ Pent- — None 182 R¹⁻² Mono- — None — None R1-R⁸ Pent- 183R¹⁻² Mono- R¹-R⁸ Pent- R¹-R⁸ Mono- — None 184 R¹⁻² Mono- R¹-R⁸ Pent- —None R¹-R⁸ Mono- 185 R¹⁻² Mono- R³, R⁶ Pent- R¹-R⁸ Mono- R¹-R⁸ Mono- 186R¹⁻² Mono- R¹-R⁸ Pent- R¹-R⁸ Di- — None 187 R¹⁻² Mono- R¹-R⁸ Pent- —None R¹-R⁸ Di- 188 R¹⁻² Mono- R¹-R⁸ Mono- R¹-R⁸ Pent- — None 189 R¹⁻²Mono- — None R¹-R⁸ Pent- R¹-R⁸ Mono- 190 R¹⁻² Mono- R¹-R⁸ Mono- R³, R⁶Pent- R¹-R⁸ Mono- 191 R¹⁻² Mono- R¹-R⁸ Di- R¹-R⁸ Pent- — None 192 R¹⁻²Mono- — None R¹-R⁸ Pent- R¹-R⁸ Di- 193 R¹⁻² Mono- R¹-R⁸ Mono- — NoneR¹-R⁸ Pent- 194 R¹⁻² Mono- — None R¹-R⁸ Mono- R¹-R⁸ Pent- 195 R¹⁻² Mono-R¹-R⁸ Mono- R¹-R⁸ Mono- R³, R⁶ Pent- 196 R¹⁻² Mono- R¹-R⁸ Di- — NoneR¹-R⁸ Pent- 197 R¹⁻² Mono- — None R¹-R⁸ Di- R¹-R⁸ Pent- 198 R¹⁻² Mono-R¹⁻⁸ Hexa- — None — None 199 R¹⁻² Mono- — None R¹-R⁸ Hexa- — None 200R¹⁻² Mono- — None — None R1-R⁸ Hexa- 201 R¹⁻² Mono- R¹-R⁸ Hexa- R¹-R⁸Mono- — None 202 R¹⁻² Mono- R¹-R⁸ Hexa- — None R¹-R⁸ Mono- 203 R¹⁻²Mono- R¹-R⁸ Mono- R¹-R⁸ Hexa- — None 204 R¹⁻² Mono- — None R¹-R⁸ Hexa-R¹-R⁸ Mono- 205 R¹⁻² Mono- R¹-R⁸ Mono- — None R¹-R⁸ Hexa- 206 R¹⁻² Mono-— None R¹-R⁸ Mono- R¹-R⁸ Hexa- 207 R¹⁻² Mono- R¹⁻⁸ Hepta- — None — None208 R¹⁻² Mono- — None R¹-R⁸ Hepta- — None 209 R¹⁻² Mono- — None — NoneR1-R⁸ Hepta- 210 R¹⁻⁸ Di- R¹-R⁸ Mono- — None — None 211 R¹⁻⁸ Di- — NoneR¹-R⁸ Mono- — None 212 R¹⁻⁸ Di- — None — None R¹-R⁸ Mono- 213 R¹⁻⁸ Di-R¹-R⁸ Mono- R¹-R⁸ Mono- — None 214 R¹⁻⁸ Di- R¹-R⁸ Mono- — None R¹-R⁸Mono- 215 R¹⁻⁸ Di- — None R¹-R⁸ Mono- R¹-R⁸ Mono- 216 R¹⁻⁸ Di- R¹-R⁸Mono- R¹-R⁸ Mono- R¹-R⁸ Mono- 217 R¹⁻⁸ Di- R¹⁻⁸ Di- — None — None 218R¹⁻⁸ Di- — None R¹-R⁸ Di- — None 219 R¹⁻⁸ Di- — None — None R1-R⁸ Di-220 R¹⁻⁸ Di- R¹-R⁸ Di- R¹-R⁸ Mono- — None 221 R¹⁻⁸ Di- R¹-R⁸ Di- — NoneR¹-R⁸ Mono- 223 R¹⁻⁸ Di- R³, R⁶ Di- R¹-R⁸ Mono- R¹-R⁸ Mono- 224 R¹⁻⁸ Di-R¹-R⁸ Mono- R¹-R⁸ Di- — None 225 R¹⁻⁸ Di- — None R¹-R⁸ Di- R¹-R⁸ Mono-226 R¹⁻⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Di- R¹-R⁸ Mono- 227 R¹⁻⁸ Di- R¹-R⁸ Mono-— None R¹-R⁸ Di- 228 R¹⁻⁸ Di- — None R¹-R⁸ Mono- R¹-R⁸ Di- 229 R¹⁻⁸ Di-R¹-R⁸ Mono- R¹-R⁸ Mono- R¹-R⁸ Di- 230 R¹⁻⁸ Di- R¹-R⁸ Di- R¹-R⁸ Di- —None 231 R¹⁻⁸ Di- R¹-R⁸ Di- R¹-R⁸ Di- R¹-R⁸ Mono- 232 R¹⁻⁸ Di- R¹-R⁸ Di-— None R¹-R⁸ Di- 233 R¹⁻⁸ Di- R¹-R⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Di- 234 R¹⁻⁸Di- — None R¹-R⁸ Di- R¹-R⁸ Di- 235 R¹⁻⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Di- R¹-R⁸Di- 236 R¹⁻⁸ Di- R¹-R⁸ Di- R¹-R⁸ Di- R¹-R⁸ Di- 237 R¹⁻⁸ Di- R¹⁻⁸ Tri- —None — None 238 R¹⁻⁸ Di- — None R¹-R⁸ Tri — None 239 R¹⁻⁸ Di- — None —None R1-R⁸ Tri 240 R¹⁻⁸ Di- R¹-R⁸ Tri- R¹-R⁸ Mono- — None 241 R¹⁻⁸ Di-R¹-R⁸ Tri- — None R¹-R⁸ Mono- 242 R¹⁻⁸ Di- R³, R⁶ Tri- R¹-R⁸ Mono- R¹-R⁸Mono- 243 R¹⁻⁸ Di- R¹-R⁸ Tri- R¹-R⁸ Di- — None 244 R¹⁻⁸ Di- R¹-R⁸ Tri- —None R¹-R⁸ Di- 245 R¹⁻⁸ Di- R¹-R⁸ Tri- R¹-R⁸ Di- R¹-R⁸ Mono- 246 R¹⁻⁸Di- R¹-R⁸ Tri- R¹-R⁸ Mono- R¹-R⁸ Di- 247 R¹⁻⁸ Di- R¹-R⁸ Tri- R¹-R⁸ Tri-— None 248 R¹⁻⁸ Di- R¹-R⁸ Tri- — None R¹-R⁸ Tri- 248 R¹⁻⁸ Di- R¹-R⁸Mono- R¹-R⁸ Tri- — None 249 R¹⁻⁸ Di- — None R¹-R⁸ Tri- R¹-R⁸ Mono- 250R¹⁻⁸ Di- R¹-R⁸ Mono- R³, R⁶ Tri- R¹-R⁸ Mono- 251 R¹⁻⁸ Di- R¹-R⁸ Di-R¹-R⁸ Tri- — None 252 R¹⁻⁸ Di- — None R¹-R⁸ Tri- R¹-R⁸ Di- 253 R¹⁻⁸ Di-R¹-R⁸ Di- R¹-R⁸ Tri- R¹-R⁸ Mono- 254 R¹⁻⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Tri-R¹-R⁸ Di- 255 R¹⁻⁸ Di- — None R¹-R⁸ Tri- R¹-R⁸ Tri- 256 R¹⁻⁸ Di- R¹-R⁸Mono- — None R¹-R⁸ Tri- 257 R¹⁻⁸ Di- — None R¹-R⁸ Mono- R¹-R⁸ Tri- 258R¹⁻⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Mono- R³, R⁶ Tri- 259 R¹⁻⁸ Di- R¹-R⁸ Di- —None R¹-R⁸ Tri- 260 R¹⁻⁸ Di- — None R¹-R⁸ Di- R¹-R⁸ Tri- 261 R¹⁻⁸ Di-R¹-R⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Tri- 262 R¹⁻⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Di-R¹-R⁸ Tri- 263 R¹⁻⁸ Di- R¹⁻⁸ Quart- — None — None 264 R¹⁻⁸ Di- — NoneR¹-R⁸ Quart- — None 265 R¹⁻⁸ Di- — None — None R1-R⁸ Quart- 266 R¹⁻⁸ Di-R¹-R⁸ Quart- R¹-R⁸ Mono- — None 267 R¹⁻⁸ Di- R¹-R⁸ Quart- — None R¹-R⁸Mono- 268 R¹⁻⁸ Di- R³, R⁶ Quart- R¹-R⁸ Mono- R¹-R⁸ Mono- 269 R¹⁻⁸ Di-R¹-R⁸ Quart- R¹-R⁸ Di- — None 270 R¹⁻⁸ Di- R¹-R⁸ Quart- — None R¹-R⁸ Di-271 R¹⁻⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Quart- — None 272 R¹⁻⁸ Di- — None R¹-R⁸Quart- R¹-R⁸ Mono- 273 R¹⁻⁸ Di- R¹-R⁸ Mono- R³, R⁶ Quart- R¹-R⁸ Mono-274 R¹⁻⁸ Di- R¹-R⁸ Di- R¹-R⁸ Quart- — None 275 R¹⁻⁸ Di- — None R¹-R⁸Quart- R¹-R⁸ Di- 276 R¹⁻⁸ Di- R¹-R⁸ Mono- — None R¹-R⁸ Quart- 277 R¹⁻⁸Di- — None R¹-R⁸ Mono- R¹-R⁸ Quart- 278 R¹⁻⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Mono-R³, R⁶ Quart- 279 R¹⁻⁸ Di- R¹-R⁸ Di- — None R¹-R⁸ Quart- 280 R¹⁻⁸ Di- —None R¹-R⁸ Di- R¹-R⁸ Quart- 281 R¹⁻⁸ Di- R¹⁻⁸ Pent- — None — None 282R¹⁻⁸ Di- — None R¹-R⁸ Pent- — None 283 R¹⁻⁸ Di- — None — None R1-R⁸Pent- 284 R¹⁻⁸ Di- R¹-R⁸ Pent- R¹-R⁸ Mono- — None 285 R¹⁻⁸ Di- R¹-R⁸Pent- — None R¹-R⁸ Mono- 286 R¹⁻⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Pent- — None 287R¹⁻⁸ Di- — None R¹-R⁸ Pent- R¹-R⁸ Mono- 288 R¹⁻⁸ Di- R¹-R⁸ Mono- — NoneR¹-R⁸ Pent- 289 R¹⁻⁸ Di- — None R¹-R⁸ Mono- R¹-R⁸ Pent- 290 R¹⁻⁸ Di-R¹⁻⁸ Hexa- — None — None 291 R¹⁻⁸ Di- — None R¹-R⁸ Hexa- — None 292 R¹⁻⁸Di- — None — None R1-R⁸ Hexa- 293 R¹⁻⁸ Tri- R¹-R⁸ Mono- — None — None294 R¹⁻⁸ Tri- — None R¹-R⁸ Mono- — None 295 R¹⁻⁸ Tri- — None — NoneR¹-R⁸ Mono- 296 R¹⁻⁸ Tri- R¹-R⁸ Mono- R¹-R⁸ Mono- — None 297 R¹⁻⁸ Tri-R¹-R⁸ Mono- — None R¹-R⁸ Mono- 298 R¹⁻⁸ Tri- — None R¹-R⁸ Mono- R¹-R⁸Mono- 299 R¹⁻⁸ Tri- R¹-R⁸ Mono- R¹-R⁸ Mono- R¹-R⁸ Mono- 300 R¹⁻⁸ Tri-R¹⁻⁸ Di- — None — None 301 R¹⁻⁸ Tri- — None R¹-R⁸ Di- — None 302 R¹⁻⁸Tri- — None — None R1-R⁸ Di- 303 R¹⁻⁸ Tri- R¹-R⁸ Di- R¹-R⁸ Mono- — None304 R¹⁻⁸ Tri- R¹-R⁸ Di- — None R¹-R⁸ Mono- 305 R¹⁻⁸ Tri- R³, R⁶ Di-R¹-R⁸ Mono- R¹-R⁸ Mono- 306 R¹⁻⁸ Tri- R¹-R⁸ Mono- R¹-R⁸ Di- — None 307R¹⁻⁸ Tri- — None R¹-R⁸ Di- R¹-R⁸ Mono- 308 R¹⁻⁸ Tri- R¹-R⁸ Mono- R¹-R⁸Di- R¹-R⁸ Mono- 309 R¹⁻⁸ Tri- R¹-R⁸ Mono- — None R¹-R⁸ Di- 310 R¹⁻⁸ Tri-— None R¹-R⁸ Mono- R¹-R⁸ Di- 311 R¹⁻⁸ Tri- R¹-R⁸ Mono- R¹-R⁸ Mono- R¹-R⁸Di- 312 R¹⁻⁸ Tri- R¹-R⁸ Di- R¹-R⁸ Di- — None 313 R¹⁻⁸ Tri- R¹-R⁸ Di-R¹-R⁸ Di- R¹-R⁸ Mono- 314 R¹⁻⁸ Tri- R¹-R⁸ Di- — None R¹-R⁸ Di- 315 R¹⁻⁸Tri- R¹-R⁸ Di- R¹-R⁸ Mono- R¹-R⁸ Di- 316 R¹⁻⁸ Tri- — None R¹-R⁸ Di-R¹-R⁸ Di- 317 R¹⁻⁸ Tri- R¹-R⁸ Mono- R¹-R⁸ Di- R¹-R⁸ Di- 318 R¹⁻⁸ Tri-R¹⁻⁸ Tri- — None — None 319 R¹⁻⁸ Tri- — None R¹-R⁸ Tri — None 320 R¹⁻⁸Tri- — None — None R1-R⁸ Tri 321 R¹⁻⁸ Tri- R¹-R⁸ Tri- R¹-R⁸ Mono- — None323 R¹⁻⁸ Tri- R¹-R⁸ Tri- — None R¹-R⁸ Mono- 324 R¹⁻⁸ Tri- R³, R⁶ Tri-R¹-R⁸ Mono- R¹-R⁸ Mono- 325 R¹⁻⁸ Tri- R¹-R⁸ Tri- R¹-R⁸ Di- — None 326R¹⁻⁸ Tri- R¹-R⁸ Tri- — None R¹-R⁸ Di- 327 R¹⁻⁸ Tri- R¹-R⁸ Mono- R¹-R⁸Tri- — None 328 R¹⁻⁸ Tri- — None R¹-R⁸ Tri- R¹-R⁸ Mono- 329 R¹⁻⁸ Tri-R¹-R⁸ Mono- R³, R⁶ Tri- R¹-R⁸ Mono- 330 R¹⁻⁸ Tri- R¹-R⁸ Di- R¹-R⁸ Tri- —None 331 R¹⁻⁸ Tri- — None R¹-R⁸ Tri- R¹-R⁸ Di- 332 R¹⁻⁸ Tri- R¹-R⁸ Mono-— None R¹-R⁸ Tri- 333 R¹⁻⁸ Tri- — None R¹-R⁸ Mono- R¹-R⁸ Tri- 334 R¹⁻⁸Tri- R¹-R⁸ Mono- R¹-R⁸ Mono- R³, R⁶ Tri- 335 R¹⁻⁸ Tri- R¹-R⁸ Di- — NoneR¹-R⁸ Tri- 336 R¹⁻⁸ Tri- — None R¹-R⁸ Di- R¹-R⁸ Tri- 337 R¹⁻⁸ Tri- R¹⁻⁸Quart- — None — None 338 R¹⁻⁸ Tri- — None R¹-R⁸ Quart- — None 339 R¹⁻⁸Tri- — None — None R1-R⁸ Quart- 340 R¹⁻⁸ Tri- R¹-R⁸ Quart- R¹-R⁸ Mono- —None 341 R¹⁻⁸ Tri- R¹-R⁸ Quart- — None R¹-R⁸ Mono- 342 R¹⁻⁸ Tri- R¹-R⁸Mono- R¹-R⁸ Quart- — None 343 R¹⁻⁸ Tri- — None R¹-R⁸ Quart- R¹-R⁸ Mono-344 R¹⁻⁸ Tri- R¹-R⁸ Mono- — None R¹-R⁸ Quart- 345 R¹⁻⁸ Tri- — None R¹-R⁸Mono- R¹-R⁸ Quart- 346 R¹⁻⁸ Tri- R¹⁻⁸ Pent- — None — None 347 R¹⁻⁸ Tri-— None R¹-R⁸ Pent- — None 348 R¹⁻⁸ Tri- — None — None R1-R⁸ Pent- 348R¹⁻⁸ Quart- R¹-R⁸ Mono- — None — None 349 R¹⁻⁸ Quart- — None R¹-R⁸ Mono-— None 350 R¹⁻⁸ Quart- — None — None R¹-R⁸ Mono- 351 R¹⁻⁸ Quart- R¹-R⁸Mono- R¹-R⁸ Mono- — None 352 R¹⁻⁸ Quart- R¹-R⁸ Mono- — None R¹-R⁸ Mono-353 R¹⁻⁸ Quart- — None R¹-R⁸ Mono- R¹-R⁸ Mono- 354 R¹⁻⁸ Quart- R¹-R⁸Mono- R¹-R⁸ Mono- R¹-R⁸ Mono- 355 R¹⁻⁸ Quart- R¹⁻⁸ Di- — None — None 356R¹⁻⁸ Quart- — None R¹-R⁸ Di- — None 357 R¹⁻⁸ Quart- — None — None R1-R⁸Di- 358 R¹⁻⁸ Quart- R¹-R⁸ Di- R¹-R⁸ Mono- — None 359 R¹⁻⁸ Quart- R¹-R⁸Di- — None R¹-R⁸ Mono- 360 R¹⁻⁸ Quart- R³, R⁶ Di- R¹-R⁸ Mono- R¹-R⁸Mono- 361 R¹⁻⁸ Quart- R¹-R⁸ Mono- R¹-R⁸ Di- — None 362 R¹⁻⁸ Quart- —None R¹-R⁸ Di- R¹-R⁸ Mono- 363 R¹⁻⁸ Quart- R¹-R⁸ Mono- R¹-R⁸ Di- R¹-R⁸Mono- 364 R¹⁻⁸ Quart- R¹-R⁸ Mono- — None R¹-R⁸ Di- 365 R¹⁻⁸ Quart- —None R¹-R⁸ Mono- R¹-R⁸ Di- 366 R¹⁻⁸ Quart- R¹-R⁸ Mono- R¹-R⁸ Mono- R¹-R⁸Di- 367 R¹⁻⁸ Quart- R¹-R⁸ Di- R¹-R⁸ Di- — None 368 R¹⁻⁸ Quart- R¹-R⁸ Di-— None R¹-R⁸ Di- 369 R¹⁻⁸ Quart- — None R¹-R⁸ Di- R¹-R⁸ Di- 370 R¹⁻⁸Quart- R¹⁻⁸ Tri- — None — None 371 R¹⁻⁸ Quart- — None R¹-R⁸ Tri — None372 R¹⁻⁸ Quart- — None — None R1-R⁸ Tri 373 R¹⁻⁸ Quart- R¹-R⁸ Tri- R¹-R⁸Mono- — None 374 R¹⁻⁸ Quart- R¹-R⁸ Tri- — None R¹-R⁸ Mono- 375 R¹⁻⁸Quart- R¹-R⁸ Mono- R¹-R⁸ Tri- — None 376 R¹⁻⁸ Quart- — None R¹-R⁸ Tri-R¹-R⁸ Mono- 377 R¹⁻⁸ Quart- R¹-R⁸ Mono- — None R¹-R⁸ Tri- 378 R¹⁻⁸Quart- — None R¹-R⁸ Mono- R¹-R⁸ Tri- 379 R¹⁻⁸ Quart- R¹⁻⁸ Quart- — None— None 380 R¹⁻⁸ Quart- — None R¹-R⁸ Quart- — None 381 R¹⁻⁸ Quart- — None— None R1-R⁸ Quart- 382 R¹⁻⁸ Penta- R¹-R⁸ Mono- — None — None 383 R¹⁻⁸Penta- — None R¹-R⁸ Mono- — None 384 R¹⁻⁸ Penta- — None — None R¹-R⁸Mono- 385 R¹⁻⁸ Penta- R¹-R⁸ Mono- R¹-R⁸ Mono- — None 386 R¹⁻⁸ Penta-R¹-R⁸ Mono- — None R¹-R⁸ Mono- 387 R¹⁻⁸ Penta- — None R¹-R⁸ Mono- R¹-R⁸Mono- 388 R¹⁻⁸ Penta- R¹-R⁸ Mono- R¹-R⁸ Mono- R¹-R⁸ Mono- 389 R¹⁻⁸Penta- R¹⁻⁸ Di- — None — None 390 R¹⁻⁸ Penta- — None R¹-R⁸ Di- — None391 R¹⁻⁸ Penta- — None — None R1-R⁸ Di- 392 R¹⁻⁸ Penta- R¹-R⁸ Di- R¹-R⁸Mono- — None 393 R¹⁻⁸ Penta- R¹-R⁸ Di- — None R¹-R⁸ Mono- 394 R¹⁻⁸Penta- R¹-R⁸ Mono- R¹-R⁸ Di- — None 395 R¹⁻⁸ Penta- — None R¹-R⁸ Di-R¹-R⁸ Mono- 396 R¹⁻⁸ Penta- R¹-R⁸ Mono- — None R¹-R⁸ Di- 397 R¹⁻⁸ Penta-— None R¹-R⁸ Mono- R¹-R⁸ Di- 398 R¹⁻⁸ Penta- R¹⁻⁸ Tri- — None — None 399R¹⁻⁸ Penta- — None R¹-R⁸ Tri — None 400 R¹⁻⁸ Penta- — None — None R1-R⁸Tri

Particularly preferred anthraquinone and anthrahydroquinoen derivativesare molecules with ID No. 87-89, 92-93, 96, 98-103, 107-110, 112, 118,211-212, 215, 217-230, 232, 234, 236-238, 241, 249, 263-264, 294-295,298, 300-310, 312, 314, 316, 318-319, 328, and 337-338.

Preferably, compositions according to the present invention comprise or(essentially) consists of at least two sulfonated (optionallylignin-derived) low molecular weight (aromatic) compounds as definedherein (preferably a mixture thereof), wherein said compounds exhibitalternative substitution patterns.

Specifically, the composition according to the invention may comprise atleast two sulfonated low molecular weight aromatic compounds arecharacterized by the following:

(a) at least one compound according to Formula (X) and (XI) as definedherein;

(b) at least one compound according to Formula (XII) and (XIII) asdefined herein; or

(c) at least one compound according to Formula (XIV) and (XIV as definedherein.

In particular, the composition may comprise

(a) at least two compounds according to Formula (X) and (XI), whereinsaid at least two compounds are distinctly sulfonated and/orsubstituted;

(b) at least two compounds according to Formula (XII) or (XIII), whereinsaid at least two compounds are distinctly sulfonated and/orsubstituted; or

(c) at least two compounds according to Formula (XIV) or (XV), whereinsaid at least two compounds are distinctly sulfonated and/orsubstituted.

The composition may comprise at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ormore compounds as defined above. Said compounds may preferably eachcomprise at least two SO₃H groups. “Distinctly sulfonated” means thatsaid compounds exhibit a different sulfonation pattern (i.e. differentresidues R in the Formulae (X)-(XV) represent SO₃H groups). Thecompounds may however also exhibit the same sulfonation pattern but havean otherwise distinct substitution pattern (e.g. different residues R inthe Formulae (X)-(XV) represent, e.g., OH or C₁₋₆ alkoxy groups).

The present inventors further discovered that compositions comprising or(essentially) consisting of mixtures of sulfonated (optionallylignin-derived) lmw (aromatic) compounds as defined herein (saidcompounds comprising different basic structural formulae and/orpreferably different substitutions patterns), exhibit electrochemicalproperties enabling their use as redox flow battery electrolytes. Thepresent invention thus inter alia has the advantage of supersedingelaborate purification steps in order to provide essentially “pure”electrolytes rather than crude mixtures thereof. A lignin-derived (orother) composition (preferably obtained by a method as disclosed herein)comprising suitable unsulfonated precursor compounds can thus as a wholebe subjected to a sulfonation reaction, yielding a compositioncomprising (at least one or a mixture of) sulfonated lmw (aromatic)compounds. They can be employed as a ready-to-use product in redox flowbatteries, or can be utilized for various other applications. Incontrast, state-of-the art technologies rely on the use of only oneredox active species that has to be provided essentially purified.

As indicated above, the compositions and compounds described throughoutthe present specification (including both precursor and targetcompositions/compounds) may be “lignin-derived” (“derived from lignin”).Thereby, compositions and compounds can advantageously be obtained fromlignin or lignin derivatives that typically occur as by-products of thepulping industry. It is however also conceivable to provide suitableprecursor (and ultimately target) compounds from fossil resources,including crude oil and coal, or from pure organic substances.

“Lignin” is generally understood herein as wood-derived heterogeneousphenolic macromolecule or, rather, a group of phenolic macromolecules ofplant origin, which is or are composed of different monomeric buildingblocks. Hence, it is understood to be a natural copolymer. Morespecifically, lignin may be generally defined as an amorphousthree-dimensional polymer, which is mainly and naturally composed ofphenolic building blocks. Lignin in its “native” state, i.e. as part ofthe natural lignocellulosic material, is the starting material of theinventive method for any “modified lignin” and, subsequently, any“lignin-derived” compositions or compounds as described herein asproduct of the inventive methods.

Lignin typically comprises p-coumaryl, coniferyl and sinapyl alcohol asthe phenolic building blocks, which are linked (randomly) with ether(C—O—C) bonds, such as “beta-O-4”, “4-O-5” and, to a less frequentextent, “1-O-4”. The most frequently seen covalent linkage in naturalsoftwood and hardwood lignin is typically the “beta-O-4” bond, whichaccounts, e.g., for approximately 45-50% of all bonds in spruce and upto 60% in birch. Additionally, carbon-carbon (C—C) linkages may occur innatural lignin, such as “5-5”, “beta-5”, “beta-beta” and “beta-1”,amongst which the “5-5” linkage is the most frequently seen C—C linkage,in particular in softwood, such as spruce. Typical linkages as“beta-O-4”, “4-O-5” and “5-5” are depicted in the following:

A “building block” as a base unit (derived from lignin) as used hereinmay preferably be understood as an organic moiety, which comprises atleast one bond to covalently link said building block to anotherbuilding block of the same or different chemical structure to form aplurality of covalently associated building blocks. Preferably, abuilding block according to the present invention is a “phenolicbuilding block”, i.e. any moiety comprising a six-membered aromaticring, covalently functionalized by at least one hydroxyl group (—OH).Hence, the lignin “building block” is typically characterized by amonocyclic, typically an aromatic moiety, with the monocycle typicallybeing substituted at at least one position. Typically, each ligninbuilding block exhibits a carbocyclic monocycle with one or twosubstituents acting as linkers to another building block and one or twosubstituents, which do not exhibit any linking function. A buildingblock corresponds to a “monomer”. A “dimer” as used herein typicallycomprises two such building blocks covalently linked. Thus, the dimer istypically characterized by two isolated monocyclic moieties covalentlylinked by a linker group or by a bond (biphenylic ring system).Biphenylic ring systems (as characteristic moiety of dimers) occur withlower frequency in plant lignin, in some plants (e.g. in spruce) withhigher frequency. More generally, any such dimeric compounds belong tothe class of bicycles.

A larger plurality of any such covalently connected or linked buildingblocks forms typically the larger 3-dimensional lignin structure. In thecontext of the present invention, a “polymer” refers to a natural ligninmolecule as it occurs in plants, e.g. as part of lignocellulosicmaterial. The lignin polymer is typically a copolymer of distinctbuilding blocks. Natural lignin's “building block” corresponds to a“monomer”. Accordingly, a building block typically is a (repeating)structural part of the natural polymer lignin. The (phenolic) buildingblock has typically 9 carbon atoms (C₉) or, less frequently seen, 8carbon atoms (C₈). Typically, the building blocks have a molecularweight of about 130 to 300 Da, preferably of 150 to 250 Da, morepreferably of 160 to 190 Da. Preferably, their basic monomeric C₉ or C₈structure is not altered in the course of the natural lignin modifyingprocess by e.g. pulping. Such building blocks may serve as the basicunit in their chemistry, providing aromatic organic target compoundsaccording to the present invention.

As used herein, the term “lignin-derived” has the broadest meaning withregard to any lignin, which underwent one or more process steps, fromprocess step (1) onwards, according to the present invention. Therein, a“derived” material has to be understood as a chemical derivative. A“lignin-derived” material may be of any molecular weight smaller thanthe natural lignin polymer, including a small molecule, i.e. a lowmolecular weight compound as used herein. In this regard, both “modifiedlignin-derived components” and “lignin-derived compounds” according tothe present invention are lignin-derived material. Accordingly, a“lignin-derived” modified lignin-derived component or a (target orprecursor) compound as defined herein, is a (macro-)molecule, whichcorresponds to or is derived from a (monomeric) building block ofnatural lignin or is a homo- or heterodimers of such (monomeric)building blocks. Such compounds are derived from natural lignin via itsmodification in step (1.2) onwards, which provides the fraction ofmodified lignin-derived components as intermediates of the inventivemethod. Subsequently, a chemical decomposition step (3) provideslignin-derived low molecular weight precursor compounds that aresubjected to a sulfonation step (5) to yield lignin-derived lowmolecular weight aromatic target compounds according to the invention.“Lignin-derived” compositions are thus comprising or (essentially)consisting of lignin-derived compounds.

In a further aspect, the present invention provides a method forproducing sulfonated lmw (aromatic) compounds and compositions derivedfrom lignin, fossil resources (such as crude oil or coal) or puresubstances. An inventive method for preparing the desired targetcompounds and compositions from lignin is described in greater detail inthe following.

Preparation of Lignin-Derived Composition

The lignin-derived sulfonated target compounds and/or target compositionwhich may be used according to the present invention are preferablyobtained by a process comprising the following steps: In a first step(1), lignocellulosic material is subjected to a pulping process;yielding modified lignin-derived components. Said modifiedlignin-derived components are isolated in a second step (2) and in athird step (3) subjected to a chemical decomposition; whereby at leastone low molecular weight lignin-derived precursor compound is obtained.In a fourth step (4), said at least one precursor compound is isolatedand optionally modified, before being subjected in a fifth step (5) to asulfonation reaction, whereby one or more —SO₃H— groups are introducedas substituents into said at least one precursor compound. Thereby, asulfonated lmw aromatic ligni-derived target compound (or a compositioncomprising the same or (essentially) consisting thereof) is obtained.Said compound or composition are envisaged for use as redox flow batteryelectrolytes. Each single step of the inventive method leading to theprovision of the desired target compound or composition are discussed ingreater detail below.

Step (1): Pulping of Lignocellulosic Material and Provision of ModifiedLignin-Derived Components

By step (1) of the inventive method, lignocellulosic material issubjected to a pulping process to yield modified lignin-derivedcomponents. That step typically involves the following sub-steps:Provision of lignocellulosic material (1.1), pulping of saidlignocellulosic material (1.2) and separating the pulp from theresulting modified lignin-derived components (1.3).

Sub-Step (1.1): Provision of Lignocellulosic Material

In step (1.1) of the inventive method, lignocellulosic material isprovided. Preferably, said lignocellulosic material is chopped.

“Lignocellulosic material”, understood to be the starting material forthe method of the present invention, may be provided as any form ofplant biomass, which naturally comprises cellulose, lignin andhemicellulose. Therein, cellulose (a polysaccharide consisting of alinear chain of several hundred to many thousands of beta(1→4) linkedD-glucose units) typically forms a scaffold of fibers together withhemicellulose. Lignin (as defined above) is typically embedded withinthis scaffold, typically without being covalently linked to celluloseand/or hemicellulose. “Hemicellulose” is any of several heteropolymericpolysaccharides, which include xylan, glucuronoxylan, arabinoxylan,glucomannan, and xyloglucan. It is typically present along withcellulose in almost all plant cell walls. In contrast to cellulose,hemicellulose usually has a random, amorphous structure with littlestrength.

The lignocellulosic material may be derived from any appropriate plantorigin, e.g. wood, fiber crops or waste paper origin. In case wastepaper is used as starting material for the inventive method, such wastepaper is typically of lower paper quality, such as newspaper paper. Itusually comprises higher amounts of residual lignin, while higherquality paper is typically lignin-free. Field crop fiber or agriculturalresidues (instead of wood fiber) may be preferred as being of moresustainable nature. However, wood is the preferred renewable source,with about 90 percent of pulp originating from wood plantations orreforested areas. Non-wood fiber sources may be employed by theinventive method as well (as far as it is for global pulp production),for a variety of reasons, including seasonal availability, problems withchemical recovery, brightness of the pulp etc. Non-wood pulp processing,however, usually requires more water and energy than wood pulp pressing.

Lignocellulosic material of known and invariant character is preferred,such that the inventive method's downstream products remain essentiallyunaltered, preferably provided in the form of chopped lignocellulosicmaterial, e.g. in the form of wood chips. “Chopped” lignocellulosicmaterial is understood—by the present invention—to be advantageouslymechanically processed starting from plant material of natural origin,such that it is chopped to smaller pieces. Said lignocellulosic materialis typically processed by any form of grinding, crushing and/or milling,which results in smaller pieces of the lignocellulosic material, i.e.the chopped lignocellulosic material, which is preferred in the contextof the present invention. It may be preferred to employ lignocellulosicmaterial with a lignin content of at least 15%, more preferred of atleast 20%, most preferred of 20 to 35%.

The lignocellulosic material used as a starting material is preferablyprovided in the form of woodchips. “Woodchips” are understood as amedium-sized solid material made by cutting, or chipping, larger piecesof wood. Characteristic values (such as water content, ash content,particle size distribution, bulk density, nitrogen content, chlorinecontent) are preferably chosen such that they fulfil generally acceptedprovisions, such as the European Standard EN 14961. Wood chips astypically used for chemical pulping processes are preferably used forthe inventive method as well as they are usually relatively uniform insize and substantially free of bark. The optimum size may vary with thewood species. Preferred sizes of the main fraction are about 3 to 45 mmwith a fine fraction, defined as particles below 1 mm, of preferablyless than 5%. Common wood chips used in pulp production, which arepreferred in the method of the present invention, are on average 12-25mm (0.47-0.98 in) long and 2-10 mm (0.079-0.394 in) thick. Damage of thewood fibers is preferably avoided, as fibers free of physical defectsare advantageous for the pulp properties. As the method of the presentinvention shares the same starting material as the pulping process, thestarting material should satisfy the requirements of both the inventivemethod as a whole and the pulping process. For roundwood it is mostcommon to use disk chippers. Therein, “roundwood” is understood asindustrial roundwood, which is commonly defined, e.g., in the FAO ForestProducts Yearbook to include all industrial wood (e.g. sawlogs andveneer logs, pulpwood and other industrial roundwood) and marketedforms, such as chips, particles or wood residues.

Accordingly, the lignocellulosic material may preferably be derivable ofwood of low silica and resin content, more preferably derivable fromnorthern woods, more preferably be derivable from the group consistingof beech, pine, birch, eucalyptus, grasses and spruce, wherein thelignocellulosic material is preferably chopped, and wherein thelignocellulosic material is more preferably provided in the form ofwoodchips.

Sub-Step (1.2): Pulping

In sub-step (1.2) of the inventive method, lignocellulosic material(preferably as provided in step (1.1)) is subjected to a pulpingprocess. Thereby, the lignocellulosic material is preferably subjectedto (a) a Kraft process or (b) a sulfite process as described herein. A“pulping process” is understood in the context of the present inventionas process of chemically and/or mechanically disjoining cellulose fibersfrom other constituents of the lignocellulosic starting material of thepulping process, such as any wood, fiber crops or waste paper. Saidpulping process preferably yields pulp and modified lignin-derivedcomponents. “Pulp” is understood herein to essentially comprise amixture of (preferably pure/enriched) cellulosic fibrous material, whichdoes not contain lignin or lignin-derived components or contains onlyminor residual amounts of lignin components (e.g. as impurities of thecellulosic fibrous material).

In contrast to pulping processes employed for manufacturing of pulp(wherein modified lignin-derived components are generally consideredby-products), the inventive method aims to valorize lignin and ligninderivatives by providing useful lignin-derived redox active species.Thus, in the inventive method, modified lignin-derived components areconsidered intermediates whereas pulp is the by-product.

The “pulping process” (also referred to as “pulp and/or papermanufacturing process”) is typically a commercially established processfor the production of pulp and/or paper in a pulp and/or papermanufacturing plant. A pulping process provides the preferably purecellulosic fibrous material (pulp). Being typically in the form offibers, pulp is usually not dissolved, but dispersed or suspended in theliquid employed in the pulping process. Due to its fibrous form, pulp istypically separated by sub-step (1.3) of the inventive method as fibrousmaterial, preferably by mechanical means, such as sieves and/orcentrifuges, from the method's process stream, which contains the(preferably dissolved, suspended and/or dispersed) fraction oflignin-derived material and which is further processed by step (2).

It is typically the aim of any “pulping process” to allow disintegrationof wood into fibrous cellulosic material, lignin and hemicelluloseproducts. This is achieved by breaking covalent bonds of 3-dimensionalpolymeric lignin macromolecules. Carbon to carbon (C—C) bonds are morestable than oxygen-carbon bonds (C—O) under conditions typically appliedfor bond breaking by the “cooking” sub-step (c) of the inventive method.Thus, cleavage of oxygen-carbon bonds is the most prevalent andimportant reaction in any typical pulping process described herein assub-step (1.2). Thereby, cooking under alkaline conditions in the Kraftprocess, under acidic conditions in the sulfite process and in organicsolvents in the organosolv process allows to break oxygen-carbon bondsof lignin. Typically, any such reaction of sub-step (1.2) producesmodified products characterized by phenolic hydroxyl groups due tocleavage of natural lignin's aryl-alkyl-ether bonds. The modifiedlignin-derived components as modified products of the pulping process,i.e. “the modified lignin-derived components”, are of lower molecularsize than the polymeric lignin starting material (natural lignin).Furthermore, such lower molecular weight lignin-derived polymers areusually more soluble or dispersible than natural lignin in the processstream leaving the pulping process of sub-step (1.2). From that processstream non-dissolved or non-dispersed pulp, which usually is the targetproduct of any commercial pulping process, may readily be separated fromdissolved and/or suspended modified lignin-derived components (asrealized by sub-step (1.3) of the inventive method).

The present invention is characterized by the advantage that it mayreadily employ by its sub-step (1.2) existing plants for pulpproduction. It is characterized by enabling commercial use of lignin (inthe art typically regarded as the major undesired by-product of pulpproduction) to provide lignin-derived sulfonated low molecular weightaromatic compounds as redox flow battery electrolytes. If required, thepresent invention may also use a smaller portion of the lignin-derivedfraction of sub-step (1.2) as energy source either for the pulpproduction or for further downstream steps. The present invention is,however, unprecedented, as it enables lignin (as abundantly availableand renewable natural material) to become the starting material for theprovision of a large diversity of organic compounds usable in redox flowbatteries.

Distinct pulping processes may be used as a matter of choice to providefeedstocks for obtaining the lignin-derived components as intermediatesof the method of the present invention. The pulping process separatesthe principle components of the lignocellulosic material, degrades thepolymers to smaller compounds and occasionally causes other chemicaltransformation, depending from the method employed.

The employed pulping processes may preferably be those overly used inthe pulp and paper industries (i.e., Kraft or sulfite process) or otherprocesses such as organosolv. Each process type has its advantages anddisadvantages. The choice of the employed pulping process of theinventive method may depend on the type of lignin-derived componentswhich are subsequently processed into valuable target compounds. Thechoice of the particular pulping process may thereby determine thetarget compositions and compounds obtainable by the inventive method.

Accordingly, the pulping process of sub-step (1.2) may preferably beselected from the group consisting of Kraft process, sulfite process,organosolv process, and lignin pyrolysis process. Other processes forseparating lignin and cellulose components from lignocellulosic startingmaterial (as described herein and known in the art) may also be used forthe reaction of sub-step (1.2) to arrive at a (modified) lignin-derivedfraction. The Kraft process or, alternatively, the sulfite process areparticularly preferred pulping processes employed in sub-step (1.2) forthe method of the invention.

Both the Kraft process (a) and the sulfite process (b) are widely knownfrom the aforementioned applications and are applied accordingly by theinventive method. They allow to separate cellulosic fibrous material(pulp), which is the target material in the production of pulp and/orpaper, from other non-cellulosic wood components, in particular ligninor, rather, the (modified) lignin-derived components. For the inventivemethod, “pulp” is neither a target product nor an intermediate. Rather,the target of sub-step (1.2) is the provision of lignin as the othermajor wood component, preferably in its modified, advantageously solubleform (“modified lignin-derived components”). Typically, the presentinvention processes modified lignin-derived components, such as “Kraftlignin”, “sulfonated Kraft lignin” or “lignosulfonate”, upon separationof the cellulose fraction, as an intermediate of the inventive method.

(a) Kraft Process

The “Kraft process” is by far the most prevalent pulping processworldwide. It is typically a high pH pulping process in aqueous solution(typically aqueous sodium hydroxide) containing one or more of salt ornon-salt agents selected from sulfide, sulfhydryl and polysulfide. Itusually further comprises a sulfate salt. Accordingly, the Kraft process(a) is typically a higher pH pulping process in the presence of anaqueous solution containing one or more of salt or non-salt agentsselected from the group consisting of sulfide, sulfhydryl andpolysulfide. One or more sulfate salt(s) is/are typically added as well.

Despite the sulfides employed, relatively little sulfur is typicallycontained in the product stream following pulping. The Kraft process isversatile in terms of the lignocellulosic starting material, which istreated in aqueous solution at elevated temperature and pressure. It isenergy efficient and recycles most of the employed reactive agents, suchas reactive agents required for the pulping process. Said process yields“Kraft lignin”. Typically, the modified lignin-derived components (Kraftlignin) have a molecular weight of about 2.000 to 5.000 Da, preferably2.000 to 3.000 Da. They may be components of the natural 3-D ligninpolymers, potentially further chemically functionalized by theintroduction of additional functional groups and linkages (e.g.stilbenes). The process chemistry surrounding Kraft process including adescription of the ways in which lignin linkages are disrupted duringthe process are described in Chakar and Ragauskas Ind Crops Prod 2004,20, 131. Gierer et al. (Wood Sci Technol. 1985, 19, 289 and Wood SciTechnol. 1986, 20, 1) describes the structural changes that occur tolignin as a result of chemical bleaching during the Kraft process.

The Kraft process may be carried out as sub-step (1.2) alternative (a)according to the inventive method. The Kraft process may preferablycomprise the sub-steps of (i) optionally pre-steaming the (preferablychopped) lignocellulosic material, wherein the (preferably chopped)lignocellulosic material is advantageously wetted and preheated withsteam, (ii) adding (preferably chopped) lignocellulosic material to anaqueous alkaline solution comprising Kraft pulping agents, one or moreof the agents preferably selected from the group consisting of a sulfidesalt, a sulfhydryl agent (in particular a sulfhydryl compound or salt),a polysulfide salt (and, typically, at least one sulfate salt isadditionally comprised by the alkaline solution as well), (iii) cookingthe (preferably chopped) lignocellulosic material, which is provided(e.g. suspended and/or dispersed)) in said aqueous alkaline solution,and (iv) optionally sulfonating the lignocellulosic material in thepresence, e.g. of sulfuric acid solution and/or sulfur trioxide.

Step (i): Pre-Steaming

By optional sub-step (i) of the Kraft process, preferably choppedlignocellulosic material (such as woodchips) may be pre-treated with hotsteam. Thereby, preferably chopped lignocellulosic material is wettedand heated, which typically renders it more susceptible to adsorbtreatment solutions as applied by subsequent sub-step (ii). Cavities offresh wood are filled with fluids and/or air. Steam pre-treatment causesthe air to expand. About 25% of the air and/or other fluids naturallyoccupying the cavities is thereby expelled from these cavities.

Step (ii): Addition of Kraft Pulping Agents

By sub-step (ii) of the applied Kraft process, the optionallypre-treated, i.e. pre-steamed and pre-heated, preferably choppedlignocellulosic material is treated, preferably at elevatedtemperatures, with an aqueous alkaline solution (“treatment solution”).Typically, the lignocellulosic material is added to the treatmentsolution. Said solution typically comprises at least one chemicallyreactive agent for the Kraft process to operate. The treatment solutionmay be a liquor known in the art as “white liquor”. The employedreactive agents may adjust the pH and/or provide nucleophilic sulfide(S²⁻) and/or bisulfide (HS⁻) ions and/or moieties. Typically, saidtreatment solution comprises a mixture of chemically reactive agentsgenerally used for Kraft pulping to provide nucleophilic sulfide and/orbisulfide ion or moiety for rupturing the embedment of lignin in thecellulose scaffold of natural lignin. The reactive sulfur containingagents are usually provided as (dissolved) salts, but they may also beprovided as non-salt agents, e.g. as (dissolved) organic compounds,which comprise one or more sulphur or sulphur-based chemicalfunctionalities. Generally, any suitable reactive agent known in the artfor use in the impregnation and cooking step of the Kraft process may beemployed according to the present invention. Other than the sulfurcontaining reagents, further agents added to the solution in step (1.2)in lower amounts are typically one or more of sodium carbonate, sodiumsulfate, sodium thiosulfate, sodium chloride, and calcium carbonate.

Preferably, either of the sulfide and/or sulfate salt comprised in thealkaline solution used in the Kraft process according to (a) is a saltwith a cationic counter ion preferably selected from the groupconsisting of sodium, calcium, magnesium and ammonium. The sulfhydryland/or polysulfide agent employed by the Kraft process according to (a)is preferably an organic, non-salt agent.

By sub-step (ii) of the Kraft process, the preferably choppedlignocellulosic material is typically initially saturated with theaqueous alkaline solution, e.g. with the fresh (“white liquor”)treatment solution or with its recycled equivalent (“black liquor”). Thestep is preferably designated as the “impregnation step”, which may beperformed before the chopped lignocellulosic material is forwarded tothe vessel for the cooking process (sub-step (iii)) to occur within thevessel. For sub-step (ii), the preferably chopped lignocellulosicmaterial is typically not exposed to elevated temperatures(corresponding to the cooking temperature), but just “pre-treated”.Accordingly, the material is not or only gently heated for thatpre-treatment step.

Additional reactive agents may be added to the treatment solution toimprove the Kraft impregnation of e.g. the employed wood chips with thecooking liquor. Anthraquinone may be used as such an additive. Ittypically acts as a redox catalyst by oxidizing cellulose and reducinglignin. It protects cellulose from its degradation and makes the lignincomponent of the starting material more water-soluble. Further, anemulsion breaker may be added in an optional soap separation step toexpedite and improve the separation of soap from the cooking liquors byflocculation, once they have been used. Soap, such as rosin soap,generally forms as by-product of the Kraft process. The soap typicallyfloats at the surface of the aqueous liquid and has to be skimmed off.The collected soap may be further processed to tall oil. Advantageously,defoamers may be employed to remove eventually formed foam and fosterthe pulp production process. Drainage of washing equipment gives cleanerpulp. Dispersing agents, detackifiers and/or complexing agentspreferably allow to keep the process vessels cleaner and to reduce thenumber of maintenance operations. Fixation agents may be used to allowfinely dispersed material to be deposited on the fibers, therebyallowing such material to be readily eliminated.

Generally, aqueous alkaline solution (“liquor”) used for impregnationmay be applied for the cooking step as well. Hence, the aqueous alkalinesolution (treatment solution) used for impregnation in sub-step (ii) inthe Kraft process—and likewise the corresponding aqueous acidic solutionfor the sulfite process—is defined as “cooking liquor” in sub-step(iii). By impregnation in sub-step (ii), the treatment solution (or“cooking liquor”) preferably penetrates into the capillary structure ofthe chopped lignocellulosic material, such that initial reactions withthe wood components start at low temperature conditions. Intensiveimpregnation supports the provision of a homogeneous cook and lowrejects. Thereby, a larger portion of lignin is yielded as soluble“Kraft lignin”. Usually, about 40-60% of all alkaline pulping liquor isconsumed for the continuous type Kraft process in its initialimpregnation step.

Preferably, the pH of the aqueous alkaline solution in sub-step (ii) ofthe Kraft process according to (a) is >10. More preferably, the pH insub-step (ii) of the Kraft process according to (a) is >12. Thetemperature of the aqueous alkaline solution in sub-step (ii) of theKraft process according to (a) is typically less than 100° C., e.g. inthe range from 70° C. to 90° C.

Step (iii): Cooking

By sub-step (iii) of the Kraft process according to (a) of the inventivemethod, the pre-treated (impregnated) preferably chopped lignocellulosicmaterial is cooked in said aqueous alkaline treatment solution asrequired. The cooking period may depend on the reaction conditions, i.e.the pH, pressure and temperature, and may further depend on the type andstrength of the employed chopped lignocellulosic material. For Kraftprocessing, the material is cooked for several hours, e.g. 3 to 9 hours.Essentially, the Kraft process breaks natural lignin's internal etherbonds by nucleophilic attack of sulfide (S²⁻) and/or bisulfide (HS⁻)ions or moieties. The function of sulfide in the Kraft process may betwo-fold: It may promote and accelerate the cleavage of ether bondsbetween neighbouring building blocks of lignin's 3-dimensional polymericstructure and it reduces the extent of undesirable condensation.

Preferably, sub-step (iii) of the Kraft process is carried out in apressurized vessel (“digester”) for at least 2 hours at a temperature ofat least 150° C. Under such conditions, pulp and modified lignin-derivedcomponents may be separated from each other. Sub-step (iii) of the Kraftprocess is preferably carried out at a pressure of at least 4 bar in thepressurized vessel, preferably at 5 to 10 bar. A pressurized vessel istypically a digester as it is commonly used in the art of chemicalpulping.

It is preferred that sub-step (iii) of the Kraft process is carried outat a temperature of 150 to 190° C., preferably 170 to 180° C. Suchtemperatures typically provide higher yields (by improved separation ofthe lignin and the cellulosic fraction) and process efficiency.Increasing the temperatures significantly beyond 200° C., in particularin combination with the applied overpressure may lead to undesiredexcessive degradation of the lignin and/or the cellulosic fraction andis unfavorable in terms of energy consumption.

Sub-step (iii) of the Kraft process is preferably carried out for 2 to24 hours, preferably 3 to 5 hours. Such conditions typically enablesatisfying yields, while still ensuring overall process efficiency.Under such conditions of the Kraft process, lignin polymers andhemicellulose are sufficiently degraded, such that their lower molecularweight (lower than the starting material's natural lignin andhemicellulose) degradation products are released from the cellulosescaffold as a result of the cooking step. Such lower molecular weightdegradation products are typically more soluble in (strongly) basicsolution than the polymers of the lignocellulosic starting material.

Sub-step (iii) of the Kraft process may be carried out either in a batchmode or in a continuous mode. For the continuous mode, thelignocellulosic starting material is fed into a digester at a rate,which allows the pulping reaction to be complete by the time thematerials exit the reactor. The continuous mode is preferred to ensurehigher throughput and improved efficiency. Digesters producing 1.000tons or more of pulp per day are common and may be used according to theinventive method.

The modified lignin-derived components obtained from sub-step (iii) ofthe Kraft process are commonly known as “Kraft lignin”. These componentsare essentially unsulfonated or at least less sulfonated than“lignosulfonate” resulting from the sulfite process according toalternative (b) of sub-step (1.2). Typically, they are more soluble inaqueous alkaline solution, preferably at a pH of greater than about 9and reasonably soluble in strongly polar organic solvents. The averagemolecular weight of the lignin-derived components is generally between1.000 and 4.000 Da, preferably 2.000 to 3.000 Da. Usually, the averagecomponent of that lignin-derived fraction comprises about 10 to 35building blocks, preferably 10 to 25 building blocks, and thus, may havea “polymerization degree” of 10 to 35, preferably 10 to 25. Thelignin-derived material typically exhibits a polydispersity of between 2and 4, although it can be as high as 8 or 9. Material of such highervalues of polydispersity may be typically employed for industrial gradeapplications, but does usually not allow its subsequent exploitation asbasic material for the provision of a larger variety of organic targetcompounds as envisaged by the invention. Accordingly, polydispersity ofthe material obtained by sub-step (iii) of the Kraft process should notgo beyond 6, preferably should be less than 5 or from 2 to 5. A“molecular formula” of C9H8.5P2.1S0.1(OCH3)0.8(CO2H)0.2 was previouslyreported for softwood Kraft lignin. About 4% by weight is typically freephenolic hydroxyl. (Lebo, S. E. et al, Lignin, Kirk-Othmer Encyclopediaof Chemical Technology, p. 18 of on-line version, (2001), John Wiley &Sons, Inc.). Kraft process-derived modified lignin-derived componentstypically also comprise biphenylic moieties, in particular when usinglignocellulosic starting material being of spruce origin. Hence, sprucemay be the preferred starting material for the inventive method, ifdimeric biphenylic target products are desired.

Step (iv): Sulfonation

In order to obtain material from the Kraft process exhibiting anincreased water-solubility over a wider pH range, i.e. for acidic andneutral pH milieu, sub-step (iv) may optionally be included into theKraft process. That sub-step is preferably a sulfonation step. Therein,sulfonating agents known in the art, such as a solution of preferablyconcentrated sulfuric acid, may be added. Aliphatic side chains aretypically sulfonated, e.g. by the introduction of sulfonyl moieties assubstituents of side chains of Kraft lignin. Sulfonation mayoccasionally also affect the aromatic rings of the Kraft lignincomponents.

By sulfonation of Kraft lignin, sulfonated modified lignin is obtained,which is herein understood as “sulfonated Kraft lignin”.

Generally, sulfonation of sub-step (iv) of the Kraft process confersincreased solubility and surfactant properties to Kraft lignin.“Sulfonated Kraft lignin” shares characteristic structural or functionalproperties with “lignosulfonate” of the sulfite process, such as watersolubility over a broader pH range. Both, Kraft process-derived“sulfonated Kraft lignin” and sulfite process-derived “lignosulfonate”are referred to as “sulfonated lignin”. Kraft process-derived“sulfonated Kraft lignin” and sulfite process-derived “lignosulfonate”are generated under distinct chemical conditions resulting in structuraldistinct lignin-derived compositions. The average molecular weight ofcomponents of “sulfonated Kraft lignin” is typically lower than theaverage molecular weight of components of “lignosulfonate” resultingfrom the sulfite process. Accordingly, the molecular weight of thecomponents of sulfonated Kraft lignin may typically be about 1.000 to4.500 Da, preferably 2.500 to 3.500 Da.

For sulfonation according to sub-step (iv) of the Kraft process,overpressure and/or increased temperature may be applied. After areaction period of preferably at least two hours, sulfonated Kraftlignin may be recovered, e.g., by water removal or by precipitation,e.g. with excess lime, as calcium lignosulfonates. As sulfonationconfers improved water solubility properties to Kraft lignin, it makessuch sulfonated lignin-derived material easier to separate in an aqueousenvironment from insoluble cellulosic material. In standard pulp and/orpaper manufacturing plants operating under the Kraft process, additionalsulfonation step (iv) (which may also be designated as “postsulfonation”for Kraft lignin) is therefore typically beneficially applied.

Sulfonation sub-step (iv) of the Kraft process is preferably carried outat a temperature below 300° C., more preferably below 200° C. Suchelevated temperatures preferably ensure both sufficiently high yields ofsulfonated reaction products, while it avoids premature, i.e.uncontrolled thermal degradation of the lignin-derived Kraft ligninmaterial. Thereby, it is ensured that the lower molecular weight (ascompared to the natural lignin polymers) aromatic lignin-derivedcomponents remain intact (without uncontrolled degradation) for theirfurther processing towards the inventive method's target compounds. Lowmolecular weight monomeric or dimeric target compounds are obtained bywell-controlled decomposition of the modified lignin-derived componentsin downstream method step (3), followed by subsequent isolation(purification) in step (4). Accordingly, the largest portion of modifiedlignin-derived components possible resulting from step (2) shall be madeavailable for controlled decomposition in downstream step (3).Otherwise, the yield of the target compound would be unfavorablyreduced.

(b) Sulfite Process

Alternatively, the “sulfite process” may be employed in sub-step (1.2),which is the second most prevalent pulping process worldwide. It istypically a low pH pulping process (although it may be conducted betweenpH 2 and 12) in aqueous solution containing one or more of salt ornon-salt agents exhibiting one or more of sulfite or bisulfite groups oranions. For the sulfite process, the lignocellulosic starting materialis treated in aqueous solution at elevated temperature and pressure. Theprocess yields “lignosulfonate”, which is typically soluble in water andin some highly polar organics and amines. Lignosulfonate is generallymore water-soluble than “Kraft lignin”. Sulfite pulping is generallyless destructive than Kraft pulping, i.e. the natural lignin polymer isdegraded to modified lignin-derived components being larger (and inparticular exhibiting a higher average molecule weight and highermonomer molecular weights) than the corresponding components in Kraftpulping. Thus, “lignosulfonate” typically has a molecular weight ofabout 3.000 to 100.000 Da, preferably 5.000 to 20.000 Da.

In contrast to the Kraft process, the sulfite process is referred to asalternative method step (b). The sulfite process may preferably comprisethe sub-steps of (i) optionally pre-steaming the (preferably chopped)lignocellulosic material, wherein the (preferably chopped)lignocellulosic material is advantageously wetted and preheated withsteam, (ii) adding the (preferably chopped) lignocellulosic material toan aqueous, preferably acidic solution comprising a sulfite and/orbisulfite salt, and (iii) cooking the (preferably chopped)lignocellulosic material, which is provided (e.g. dispersed or and/orsuspended) in said aqueous, preferably acidic, solution.

In the sulfite process, the resulting solid cellulose fibers areobtained by using salts of sulfurous acid to separate the ligninfraction from natural lignocellulosic starting material, such as woodchips, e.g. in digesters preferably operating at larger pressure. Thesalt anions used in the pulping process may either be sulfites (SO₃ ²⁻),and/or bisulfites (HSO₃ ⁻), depending on the pH. At lower pH, i.e. understronger acidic conditions, such as less than pH 2.5, the sulfite istypically provided as HSO₃. Counter cations may be sodium (Na+), calcium(Ca²⁺), potassium (K⁺), magnesium (Mg²⁺) or ammonium (NH₄ ⁺).Particularly divalent (e.g. earth alkali) cations, such as calciumand/or magnesium, may be used as the counter cation. Sulfite pulping ispreferably carried out under acidic conditions, preferably at a pH below5, preferably from pH 1.5 to 5 or 1.5 to 4. The (acidic) pH may beadapted depending on the nature of the counter cation for the sulfite(bisulfite) anion. The preferred salt is calcium bisulfite, which mayadvantageously be employed, if the selected pH value for the sulfiteprocess is 2.5 or less. Higher pH sulfite pulping (at a pH above pH 2.5or, more specifically, above pH 4) generally employs monovalent ions,such as sodium or ammonium, as counter cations. However, it is notexcluded that sulfite pulping may be carried out over a wider pH range,including alkaline conditions of about pH 7 to 12.

Step (i): Pre-Steaming

Optional sub-step (i) of the sulfite process is conducted as is sub-step(i) in the Kraft process (see above). Therefore, preferably choppedlignocellulosic material (such as woodchips) may be pre-treated with hotsteam. Thereby, the preferably chopped lignocellulosic material iswetted and heated, which typically renders it more susceptible to adsorbtreatment solutions as applied by subsequent sub-step (ii). Cavities offresh wood are filled with fluids and/or air. Steam pre-treatment causesthe air to expand. About 25% of the air and/or other fluids naturallyoccupying the cavities is thereby expelled from these cavities.

Step (ii): Addition of Sulfite or Bisulfite Salt

In sub-step (ii) of the sulfite process, the lignocellulosic materialmay be brought into contact with an aqueous, preferably acidic sulfiteand/or bisulfite containing solution used as a pulping reactive agent(or “pulping liquor”).

The “pulping liquor” used in sub-step (ii) of the sulfite process may beprovided as follows: Sulfur may be oxidized (burnt) with thestochiometrically adequate amount of oxygen to yield sulfur dioxide.Sulfur dioxide is preferably added, e.g. as a gas, to water to givesulfurous acid, which may be further diluted for its use as “pulpingliquor”.

Preferably, the sulfite or bisulfite salt comprised in the aqueous(preferably acidic) solution in step (ii) of the sulphite process is asalt with a cationic counter ion preferably selected from the groupconsisting of sodium, calcium, magnesium and ammonium. The preferredsalt is calcium bisulfite.

For sub-step (ii) of the sulfite, the pH of the aqueous preferablyacidic solution is preferably 1 to 5 and more preferably 1.5 to 4. Thetemperature of the aqueous (preferably acidic) solution in sub-step (ii)of the sulfite process is also typically less than 100° C., e.g. from70° C. to 90° C.

Step (iii): Cooking

The lignocellulosic material may be brought into contact with thepulping reactive agents for more than three hours, preferably 4 to 14hours.

Sub-step (iii) of the sulfite process according to (b) is preferablycarried out at a temperature of 120 to 170° C., more preferably at atemperature of 130 to 160° C. The temperature is thus typically above120° C., preferably ranging from 130 to 160° C., depending on thereactive agents and their concentrations used.

Preferably, cooking in sub-step (iii) of the sulfite process is carriedout in a pressurized vessel for at least 3 hours at a temperature of atleast 120° C. Under such conditions, pulp and modified lignin-derivedcomponents may be separated from each other. Sub-step (iii) of thesulfite process according to (b) is preferably be carried out at apressure of at least 4 bar in the pressurized vessel, preferably at 5 to10 bar. A pressurized vessel is typically a digester as it is commonlyused in the art of chemical pulping.

Preferably, sub-step (iii) of the sulfite process is carried out for 2to 24 hours, preferably 4 to 6 hours.I

Preferably, sub-step (iii) of the sulfite process is carried out eitherin a batch mode or in a continuous mode. For the continuous mode, thelignocellulosic starting material is fed into a digester at a rate,which allows the pulping reaction to be complete by the time thematerials exit the reactor. The continuous mode is preferred to ensurehigher throughput and improved efficiency. Digesters producing 1.000tons or more of pulp per day are common and may be used according to theinventive method.

The modified lignin-derived components resulting from the sulfiteprocess are generally designated as “lignosulfonate”. Due to the natureof the sulfite process, “lignosulfonate” typically contains significantamounts of sulfur-based moieties (typically in the form of sulfonategroups), for example, in the aliphatic side chains of the modifiedlignin-derived components.

“Lignosulfonate” is thus a complex (heterogeneous) mixture of modifiedlignin-derived components, i.e. water-soluble anionic lignin-derivedpolyelectrolytes, which carry —SO₃H functional groups. Lignosulfonatetypically exhibits by its heterogeneous components a broad molecularweight range (broader than observed for Kraft lignin). Lignosulfonate ispolydisperse with a polydispersity being typically higher than that ofthe Kraft process (about 4 to 9). As the sulfite process is lessdestructive than Kraft pulping, it does not degrade lignin to the sameextent as the Kraft process. Thus, sulfite process-derivedlignosulfonate typically has a higher average molecular weight thanKraft lignin as described herein. A maximum molecular weight of 140.000Da is reported for softwood lignosulfonates, while maximum values forhardwoods are usually lower, e.g. lower than 50.000 Da. The typicalrange of the molecular weight for lignosulfonate polymers is about 5.000to 50.000 Da, preferably about 5.000 to 20.000 Da (Brogdon, B. N.,Dimmel, D. R. J. Wood Chem. Technol. 1996, 16, 297). Usually, itcomprises about 10 to 300 building blocks, preferably 20 to 200, mostpreferably 25 to 150 building blocks, and thus, may have a“polymerization degree” of 10 to 300, preferably 20 to 200, mostpreferably of 25 to 150. It typically exhibits a higher sulfur content(about 3% to 8% w/w) than (unsulfonated) Kraft lignin (having a sulfurcontent of typically less than 1% w/w).

Lignosulfonates are used in the art as low-value chemicals in tanningleather, making concrete, drilling mud and drywall, such as binders oradditives for building material.

Sulfite process-derived lignosulfonates are typically soluble in waterover essentially the entire pH range. Sulfite process-derivedlignosulfonate may also be soluble in highly polar organic and aminesolvents. Its approximate “molecular formulas” are described asC9H8.5O2.5(OCH3)0.85(SO₃H)0.4 for softwood or as C9H7.5O2.5(OCH3)1.39(SO₃H)0.6 for hardwood, respectively, as starting material forsulfite process-derived lignosulfonate. Sulfite process-derivedlignosulfonate may comprise biphenylic moieties for some of thecomponents of the larger number of components representing the“lignosulfonate” fraction. That holds specifically for lignocellulosicmaterial of spruce origin. Hence, spruce may be the preferred startingmaterial for the inventive method, if biphenylic precursor or targetcompounds are desired.

(c) Alternative Methods

Organosolv Process

As a further alternative, the “organosolv process” is typically carriedout by treatment of wood or bagasse with various organic solvents.“Bagasse” is the fibrous residue that remains once plant material (suchas sugar cane) has been crushed and juice or sap have been extracted.The “Alcell process” is one of the most well-known organosolv processes.It finally involves dissolution of lignin in either ethanol orethanol/water mixtures. The advantage of the organosolv process is thatit allows to automatically generate separate process streams ofcellulose, hemicelluloses, and lignin. Thereby, all components of thelignocellulosic biomass starting material may be individually processed.That process is generally considered as environmentally attractive, asit does not employ aggressive reactive agents (e.g. sulfides) and harshconditions used in the more common Kraft or sulfite processes. Theorganosolv process typically yields organosolv lignin as the modifiedlignin-derived components, which may be employed in further downstreamreaction steps of the present invention. Organosolv lignin is thereforetypically low in sulfur content. It has a low molecular weight of about1.000 to 2.000 Da. It is typically also of higher purity than thelignin-derived components obtained from other pulping processes. Adisadvantage of the organosolv process are the costs of solventrecovery.

Steam Explosion Process

Another pulping process, which may be employed by the present invention,is the “steam explosion process” involving steam impregnation underpressure followed by rapid pressure release, which separates thelignocellulosic constituents. Covalent linkages of 3D lignin areruptured as well, such that a complex mixture of lignin derivedfragments is obtained. Typically, wood or bagasse is exposed to steam atoverpressure and elevated temperature, such as a total pressure of 1.38to 3.45 MPa and a temperature from about 180° C. to about 230° C. forabout 1-20 min before rapid pressure release. The molecular weightdistribution of the lignin fragments obtained by the steam explosionprocess is typically similar to the organosolv process. In addition, theprocess uses no sulfur, and separating the process streams is alsopossible.

Pyrolysis

Pyrolysis of lignocellulosic material (as a further alternative ofsub-step (1.2)) generally leads to pyrolyzed lignin-derived fragments,which may also be considered as modified lignin-derived components to beemployed by the present invention. The pyrolysis process typicallyinvolves relatively high temperatures, typically at least 600 K, such asbetween 720 and 750 K. No waste other than flue gas and ash is producedby that process, whereas increased energy consumption is required tofuel the process. Pyrolysis lignin exhibits structural characteristicssignificantly different from lignin components obtained from other“pulping processes”. It involves C₈- rather than C₉ building blocks,potentially allowing for unique downstream reactions according to thepresent invention. Thereby, specific aromatic hydrocarbons are madeavailable as target compounds, which are not available via otherprocesses.

Other Methods

Several other methods for isolating (modified) lignin from wood or plantbiomass or starting material are described in the art as well, includingthe “ammonia fiber explosion” (AFEX) process and the “hot waterprocess”, which may also be employed as sub-step (1.2), which aredescribed in further detail by Bozell et al. (Top Value Added Candidatesfrom Biomass. Volume II: Results of Screening for Potential Candidatesfrom Biorefinery: Lignin; Pacific Northwest National Laboratory:Richland, W A, 2007) and Kamm et al. (Biorefineries—Industrial Processesand Products; VCH: Wcinheim, Germany, 2006; Vol. 2). Finally, the“dilute acid process” as a further option for sub-step (1.2) of theinventive method may ensure effective separation of lignin from otherbiomass components. It may, however, provide lower yields. Corrosion ofequipment (due to the acidic environment) may also be an issue. The“alkaline oxidation process” may use O₂ or H₂O₂ to degrade lignin.However, the process may suffer from slower delignification rates. Thedilute acid process and alkaline oxidation process may both providemodified lignin-derived components with similar molecular weight(distributions) as organosolv lignin.

Lignin-Derived Components

Generally, modified lignin-derived components, such as (sulfonated)“Kraft lignin” and/or “lignosulfonate”, are typically dissolved ordispersed in the consumed pulping liquor, once processed according tosub-step (1.2). Said liquor (process stream leaving step (1.2)) usuallyalso comprises most of the hemicellulose and/or its hydrolysis products(poly-, oligo and/or monosaccharides) in dissolved form.

The lignin-derived fraction of any pulping process is preferablyforwarded to separation sub-step (1.3) for its further processingtowards the low molecular weight target compound. In particular, “Kraftlignin” upon application of sub-steps (i) to (iii) of the Kraft processaccording to (a), or “lignosulfonate” upon application of the sulfiteprocess according to (b) or “sulfonated Kraft lignin” upon applicationof sub-steps (i) to (iv) of the Kraft process according to (a) may beemployed for further processing by sub-step (1.3).

Further downstream, the method of the present invention thus typicallyemploys the steps of separating pulp in sub-step (1.3) from the processstream and, subsequently, isolating the fraction of modifiedlignin-derived components in step (2) from other components beingpresent in the process stream.

Sub-Step (1.3): Pulp Separating Step

In step (1.3), the pulp obtained in sub-step (1.2) is separated in apulp separating step from the process stream obtainable from the pulpingprocess in sub-step (1.2), to provide a substantially pulp-free processstream.

Hereby, the process stream of sub-step (1.2) is converted to (i) anessentially pulp-free stream with enriched fractions of modifiedlignin-derived components, hemicellulose and/or fragments of any thereofand/or inorganic material, and (ii) pulp, which is understood herein toessentially comprise a mixture of (enriched) cellulose fibrous material.

The pulp fraction may be separated by sub-step (1.3) as dry matter or asa pulp containing stream. Sub-step (1.3) may be carried out by anysuitable separation method preferably selected from the group consistingof blowing, sieving, countercurrent flow, centrifugation, filtration,washing, stripping, ion-exchange, or any combination thereof. Separationof the pulp from the process stream is more preferably carried out byblowing, sieving and/or washing.

The pulp or pulp containing stream is further processed according tostate-of-the-art technologies for, e.g., manufacturing paper. Thestream(s) containing the fraction of modified lignin-derived componentsis subjected to step (2) of the inventive method for isolation of saidmodified lignin-derived components.

As used herein, a “stream” or “process stream” is generally understoodas a liquid medium comprising intermediates of the inventive methodresulting from the preceding method step, which serve as starting(process) material for the subsequent method step. Generally, the streamincludes its components dissolved, suspended or dispersed in said liquidmedium. Distinct fractions of the (process) stream may be obtainedreflecting components of homogenous nature, which may be isolated byfractionation from the process stream.

A “fraction” may represent a part of a whole or, more generally, anynumber of (equal) parts. In particular, a fraction is understood hereinto be a part of a (process) stream according to the present invention,which typically comprises at least two different fractions.

Accordingly, different fractions may be organic matter comprising(residual) cellulosic material and non-cellulosic material such asmodified lignin-derived components (e.g. Kraft lignin or lignosulfonate)and hemicelluloses. Further, fractions of a stream according to thepresent invention may be inorganic reactive agents, which are requiredto run the process, e.g. inorganic buffer salts. Another fraction,typically the largest both in terms of volume and mass, is thesolvent/dispersant. The solvent usually is an aqueous solvent/dispersantfrom the pulping process, which may be diluted or concentrated in thesteps following sub-step (1.2), which is herein understood to form apart of the total dry mass carried in the stream according to thepresent invention. A particularly important fraction of the stream inthe context of the present invention is the fraction of modifiedlignin-derived components.

As a derivative of natural lignin, the “modified lignin-derivedcomponent” is a lignin molecule, which underwent a pulping process, suchas “Kraft lignin” or “lignosulfonate”. A “modified lignin-derivedcomponent” typically has a lower molecular weight than natural lignin,from which it is derived. However, the “modified lignin-derivedcomponent” is larger than the low molecular weight lignin-derivedcompound, preferably having a molecular weight of at least 1.000 Da. Thenature (and the actual molecular weight) of the “modified lignin-derivedcomponent” may vary largely depending, e.g., on the starting material,on the (pulping) method, by which the modified lignin-derived componentis obtained, and on the reaction conditions applied by the inventivemethod. However, it is common to the modified lignin-derived componentsthat they are composed of C8 or C9 building blocks after, e.g., apulping process, as they occur in natural lignin.

It follows from natural lignin's complex and somewhat random chemicalstructure that lignin-derived components, such as products of thepulping process, are typically heterogeneous. The pulping processprovides a larger variety of lignin-derived components, which maytypically contain from 8 to 150 building blocks. Moreover,lignin-derived components of the same number of building blocks are alsodiverse in terms of their chemical nature, as they reflect individualportions of the heterogeneous natural lignin polymer. That chemical andstructural heterogeneity of lignin-derived material obtained from e.g.the pulping process traditionally impeded the preparation of homogeneousand/or high quality products by prior art methods, such that adequateeconomic exploitation of lignin-derived material was difficult toachieve in the art. That prior art issue is overcome by the inventivemethod.

Pulping processes, nevertheless, typically yield “modified”lignin-derived components based on C₈ or C₉ building blocks, whereinsome or all of the building blocks may be modified. Modificationspreferably occur at the linking groups of those building blocks ofnatural lignin, which are dissociated by the pulping process, and/or atsubstitution sites of the building blocks, in particular at the aromaticring system of a building block, e.g. by side chain modification or e.g.by sulfonation. Accordingly, the molecular weight of the modifiedbuilding blocks of lignin-derived components may typically be slightlyhigher than the molecular weight of the building blocks of the naturallignin polymer.

Typically, “modified lignin-derived components” as used herein arepresent as a fraction of a (process) “stream”. Such a stream maycomprise residual or waste material and the solvent and/or dispersantfrom which the intermediate of interest is preferably isolated.Typically, the solvent and/or dispersant accounts for at least 50% (w/w)of the total weight of material forwarded as a “stream” to the nextmethod step, or at least 60% (w/w), preferably for at least 70% (w/w),or at least 80% (w/w). The solvent and/or dispersant is typically anaqueous medium, but may alternatively be an organic solvent, dependingon the pulping process. Generally, the stream flows unidirectionally,from the preceding method step to the more downstream method steps.Valves, pumps and/or gravity-assisted means may typically be employed tofacilitate the required flow of the stream downwards to the final stepof the method of the present invention.

Typically, upon pulping, the lignin in the lignocellulosic material isbroken into smaller molecules, which are more soluble in the pulpingliquid. Cellulose is degraded to a minor degree, although individualcellulose fibers may detach from the chopped lignocellulosic materialduring the pulping process and dissolve rather in the pulping liquidthan natural lignin. As a consequence, a residual cellulosic scaffoldremains. However, to a varying degree, cellulose fibers are also presentin the liquid in dispersed form, i.e. not in the larger scaffoldstructure of fibers.

In sub-step (1.3) of the inventive method, preferably both the scaffoldand the dispersed cellulose fibers are separated from the processstream. A preferred way of separating the cellulose which is present inthe scaffolds, is “blowing” the cellulose scaffold of the choppedlignocellulosic material, which underwent the pulping of sub-step (1.2),into a collection tank (“blow tank”). The residual cellulosic scaffoldsmay be blown into a blow tank that usually operates at atmosphericpressure. This blowing typically releases steam and volatiles. Volatilesare understood herein as organic chemicals that have a high vaporpressure at ordinary room temperature. Typically, they are characterizedby an individual odor. The volatile fraction may be condensed andcollected. When employing “northern softwoods” as the starting materialfor the present invention, the volatile fraction typically encompassesraw turpentine.

The pulp separation in sub-step (1.3) may preferably further comprise toseparating cellulose from the liquid, which was not blown out as part ofthe blown out residual cellulosic scaffold, e.g. the dispersed cellulosefibers. The pulp separation according to sub-step (1.3) may encompassdistinct sieves or screens and/or centrifugal separation. The sieves aretypically arranged in a multistage cascade-like assembly. By such anarrangement, considerable amounts of pulp is preferably captured, andthus, separated from the process stream containing the fraction ofinterest according to the inventive method, i.e. the fraction ofmodified lignin-derived components.

The process stream (optionally subject to blowing, sieving and/orfiltration) may also undergo one or more washing steps to separate pulp.Thereby, (residual) dispersed cellulose fibers are separated from theprocess stream. Usually, a pulp mill encompasses 3-5 washing stages inseries. Pulp washing as used herein is typically carried out by pulpwashers using counter-current flow in between two subsequent stages suchthat the pulp moves in the opposite direction to the flow of washingwater. While the washing water becomes a part of the process streamcomprising the target modified lignin according to the presentinvention, cellulose is effectively separated and ready for conventionaluse such as paper production. Various techniques may be involved in pulpwashing, such as thickening/dilution, displacement and diffusion. Thewashing equipment may comprise, for example, pressure diffusers,atmospheric diffusers, vacuum drum washers, drum displacers and washpresses.

Said pulp separation step or steps may provide an essentially pulp-freeprocess stream as a result of sub-step (1.3). Therein, the essentiallypulp-free process stream, which contains the modified lignin-derivedcomponents, may be provided as one single process stream (a) or may bepartitioned in at least two (partial) process streams (b) in a furtherstream separation step.

By said stream separation step, the sum of the flow rates of the partialstreams is typically equal to the flow rate prior to the streamseparation step. The flow rate of each of the two or more partialstreams may correspond to e.g. up to 50%, 33%, and 25% etc. of the flowrate of the initial pulp-free process stream prior to the division.Alternatively, one of the partial streams may exhibit a higher flow ratethan the other partial stream(s). Typical percentile ratios of flowrates may be 5:95, 10:90, 15: 85, 20:80, 25:75, 30:70, 35:65, 40:60 and55:45. When dividing e.g. into three partial streams, each processstream may have a flow rate corresponding to one third of the flow rateof the stream. Alternatively, one or two partial streams may have a flowrate higher or lower than the third stream, provided that the sum of theflow rates of the partial streams preferably equals the flow rate of theinitial stream. Thereby, e.g. modified lignin-derived componentscomprised in all partial streams may be simultaneously supplied to(conventional) combustion as an energy source, to further processingaccording to the inventive method and, e.g., to storage facilities, e.g.a container. Hence, said stream division may provide a “buffer capacity”depending on the status of the plant and the turnover of the method as awhole, which adds versatility and efficiency to the method, preferablywithout generating extra waste.

Separating the stream for further processing in downstream steps may becarried out by technical means known in the field of fluid processtechnology. Preferably, the separation means are adjustable in such away, that defined portions of the single process stream according to (a)may be mechanically divided into two or more, three or more or four ormore partial streams. The means for dividing may be selected from aflap, hatch, clack, lid, valve, damper or shutter or a combinationthereof. Said means may operate electrically and/or hydraulically.Alternatively, the stream may be divided into partial streams by vacuumand/or pressurized gas, i.e. portions of the stream may be sucked orblown into two or more passages. Therein, a passage is understood as anyform of duct, which passes the respective stream to its next stage. Thedividing means and/or of the passages conducting the partial processstreams are typically made of non-corroding metal, preferably coated ornon-coated stainless steel.

The essentially pulp-free stream, which is herein forwarded for itsfurther processing in step (2), is commonly designated as “black liquor”(due to its color), when applying the Kraft process or “brown liquor”,when applying the sulfite process in step (1.2). It typically comprisesmodified lignin-derived components and random fragments thereof (i.e.lignin-derived molecules formed during the pulping process, but having alower molecular weight than the typical modified lignin-derivedcomponents) and hydrolysis products of hemicellulose. Hemicellulose istypically hydrolyzed in any pulping process, e.g. in acidic or alkalinemedium, yielding smaller pieces of hemicellulose such as poly- oroligosaccharide fragments or even mono- or disaccharides thereof, whichare all usually dissolved in the pulping liquid and/or the processstream. Further, (in)organic salts as residual components of thereactive agents used for the pulping process may be comprised in theessentially pulp-free process stream, such as sodium carbonate and/orsodium sulfate.

Step (2): Isolation of Modified Lignin-Derived Components

After the pulping process according to sub-step (1.2), the fraction ofmodified lignin-derived components comprised either in the singleprocess stream provided by sub-step (1.3(a)) or in at least one of theat least two (partial) process streams provided by sub-step (1.3(b)) isisolated from the process stream(s) and its/their other components (e.g.hemicellulose and/or hydrolysis products thereof). Dividing the productstream into partial product streams adds flexibility to the control ofthe yield envisaged for the fractions comprised in the essentiallypulp-free process stream. Modified lignin-derived components are thuseither isolated from the single process stream (obtained from 1.3(a)) orfrom at least one of the at least two partial process streams (obtainedfrom 1.3(b)) Therefore, by alternative (b), isolation of the fraction ofmodified lignin-derived components is applied to one or more of thepartial streams provided at the stage of sub-step 1.3(b).

In other words, isolation of modified lignin-derived components asdescribed below may be accomplished from a single process streamobtained from sub-step (1.3 (a)) or from one of several (partial)process streams obtained from sub-step (1.3(b). Several process streamsare provided from the single process stream of (1.3(a)) by separating(or dividing) said process stream into two or more (partial) streams.This allows to control the amount of the modified lignin-derivedcomponents further processed according to the inventive method. Hence,stream separation is a tool to fine tune the inventive method whendetermining its flow rate and turnover of the process. By dividing thestream into two or more partial streams, supply of modifiedlignin-derived components either to downstream process steps (3) and (4)may be controlled as well.

Modified lignin-derived components present in either a single processstream or in two or more (partial) process streams obtained fromsub-step (1.3) are isolated from said process stream(s) as describedbelow.

Isolation, i.e. controlled removal, of the fraction of modifiedlignin-derived components from the process stream(s) may be controlledby the isolation means applied, e.g. by the parameters applied (e.g. theamount of precipitation agent, pH, extraction or filtrationcharacteristics. Isolation may be applied to all or part of the partialprocess streams (if present). Typically, the essentially pulp-freeprocess stream provided by sub-step (1.3) is divided into two partialprocess streams (1.3(b)), with one of them subjected to isolation of thefraction of modified lignin-derived components from the process streamand the other partial process streams being used for combustion and/orother uses.

In particular, the fraction of modified lignin-derived components may beisolated from the solvent and/or dispersant of the process stream, suchthat the fraction of modified lignin-derived components may be obtainedas dry matter. It may then be re-dissolved in a suitable solvent ordispersed in a suitable dispersant, e.g. an aqueous solvent ordispersant, to be further processed in the subsequent method step.Alternatively, the fraction of modified lignin-derived components may beenriched, e.g. by reducing the solvent and/or dispersant content of thefraction of modified lignin-derived components, such that a concentratedsolution or dispersion is provided.

Isolation of step (2) may be carried out by any appropriate meansemployed in the field of solid-fluid or fluid-fluid separation. Theisolation may, for example, involve filtration, extraction, countercurrent flow separation and precipitation. Any technology may be usedaccording to step (2) of the invention to control the amount of isolatedmodified lignin-derived components, which may then be subjected tofurther processing.

Step (2), i.e. isolation of the fraction of modified lignin-derivedcomponents from other (e.g. hemicellulosic) components in the processstream, may preferably be carried out by filtration including ultra-and/or nanofiltration, extraction, countercurrent flow, stripping,ion-exchange, precipitation by di- or multivalent cations, such ascalcium cations (which may e.g. be provided as calcium hydroxide),precipitation by CO₂ in acidic solution, or any combination of thereof.

(a) Filtration

Preferably, isolation is carried out by any type of extraction orfiltration, preferably ultrafiltration and/or nanofiltration.

“Filtration” is hereby understood as a physical purification orenrichment method involving membrane technology by permeable membranes.Membranes are characterized by their nominal pore size. It typicallydescribes the maximum pore size distribution. As that parameter providesonly vague information about the retention capacity of the membrane, the“cut-off” is typically used as the parameter to characterize separationproperties of membrane-associated filtration. The exclusion limit or“cut-off” of the membrane is usually specified in the form of NMWC(nominal molecular weight cut-off, or MWCO, molecular weight cut off,with units in Dalton). It is commonly defined as the minimum molecularweight of a globular molecule that is retained to 90% by the membrane.In practice, the MWCO of the membrane should be at least 20% lower thanthe molecular weight of the molecule that is to be separated. Forexample, a 1 kDa filter is suitable to let pass a small molecule with amolecular weight of, e.g., 500 Da, while the larger modifiedlignin-derived components of a molecular weight of, e.g., 2.000 Da arenot able to pass.

Preferably, filtration is used herein to isolate, in step (2), thedispersed or suspended modified lignin-derived components obtained instep (1). The filter cut-off is set in such a way, that it is suitableto discriminate the molecular weight of the target modifiedlignin-derived components and of other components in the process stream.The other components may be larger (e.g. residual natural lignin and/orfragments thereof having a higher molecular weight than the modifiedlignin-derived components) or smaller (e.g. reactive agents of thepulping process, hydrolyzed hemicellulose) than the target components.If the target modified lignin-derived components are of a largermolecular weight than all other components in the process stream, thefilter is selected to have a cut off such that the target components aretypically retained in the filter. Otherwise, if other components arelarger—in terms of molecular weight—than the modified lignin-derivedcomponents, the cut-off may typically be selected such that the targetcomponents may typically be found in the filtrate.

Typically, the filtration in isolation step (2) may be a combination of(different) filtration steps. Therein, for example, in one step the cutoff of the filter is selected to be higher than the molecular weight ofthe modified lignin-derived components. Accordingly, other componentswith a higher molecular weight are kept in the filter and themodified-lignin-derived components remain in the filtrate, i.e. in theresidual process stream. In another step, the residual process streammay be subjected to a second filtration, wherein the cut-off is selectedto be lower than the molecular weight of the modified lignin-derivedcomponents. Accordingly, the target modified lignin-derived componentsare retained in the filter and, thereby, isolated from the residualprocess stream. Thereby, the target components may be obtained as drymatter and may subsequently be dissolved for further processing.

The more the different fractions within the process stream differ interms of their molecular weight, the more effective may the isolation byfiltration be carried out. For example, as the Kraft process typicallyyields modified lignin-derived components (Kraft lignin) of lowermolecular weight than the sulfite process, filtration may be verypreferred to separate Kraft lignin from lignin-derived material ofhigher molecular weight, such as non-modified or re-polymerizedlignin-derived material or other debris in step (2).

Ultrafiltration and/or (depending on the size of the lignin-derivedcomponents to be isolated) nanofiltration may be preferably employed instep (2). Ultrafiltration typically employs a pore size of 2-100 nm anda molecular weight cut-off value of about 5 kDa. Nanofiltrationtypically refers to a filtration mode based on a pore size of 1-2 nm anda molecular weight cut-off value of 0.1-5 kDa. Accordingly,ultrafiltration is typically employed to separate or isolate largerlignin-derived components (e.g. larger than 5.000 Da, larger than 8.000Da or larger than 10.000 Da) from the process stream (containingcomponents of whatever e.g. the lignin-derived fraction or residualcellulosic fraction or the hemicellulosic fraction of a molecular weightof less than 5.000 Da). That isolated larger molecular weight fractionmay be subject to further separation in order to separate largerisolated components of distinct fractions, e.g. to isolate thelignin-derived components from residual cellulosic degradation productsor hemicellulosic components. The isolated lignin-derived fraction ofthe molecular weight retained by the chosen cut-off value of theultrafiltration device may then be further processed in step (3).

Also, the remaining components of the lignin-derived fraction in theprocess stream having a molecular weight lower than the cut-off levelchosen for initial ultrafiltration may be isolated from other componentsin the process stream. E.g. the (partial) process stream may besubjected to another filtration step with a lower cut-off level thanchosen for the initial ultrafiltration step, e.g. by additional lowercut-off level ultrafiltration and/or nanofiltration. Thereby, thelignin-derived components of a molecular weight lower than thecut-off-level of the first filtration step and larger than the cut-offlevel of the second filtration step may be isolated. That retainedlignin-derived fraction may be subject to further isolation to separatethe lignin-derived component fraction from components of similar size ofother fractions (e.g. from hemicellulosic degradation products ofsimilar size). Accordingly, the inventive method may be set up such thatcomponents of the lignin-derived fraction are isolated, which fallwithin the individually desired smaller molecular weight range of e.g.between 1.000, 2.000, 3.000, 4.000, 5.000 or 6.000 Da (cut-off level ofthe second filtration step) and 5.000, 6.000, 8.000 or 10.000 Da(cut-off level of the first filtration step). Thereby or by any othermethod known in the art to separate by molecular weight or by otherphysico-chemical parameters, a more homogeneous lignin-derived fractionmay be forwarded to decomposition step (3).

Accordingly, two ultrafiltration steps or ultrafiltration andnanofiltration, respectively, may e.g. be combined to arrive at amodified lignin-derived fraction of a defined molecular weight range(e.g. 5.000 to 10.000 or 1.000 to 5.000 Da, respectively for Kraftlignin). Whenever isolation from the process stream of the sulfiteprocess-derived lignosulfonate is concerned, such isolation maypreferably be performed by employing suitable isolation methods, e.g. asdescribed by Lebo et al. (Lebo, Stuart E. Jr.; Gargulak, Jerry D.;McNally, Timothy J. (2001). “Lignin”. Kirk-Othmer Encyclopedia ofChemical Technology. Kirk Othmer Encyclopedia of Chemical Technology.John Wiley & Sons, Inc.), which is incorporated herein by reference.“Lignosulfonate” (due to the larger molecular weight of its components)will preferably be based on two ultrafiltration steps resulting e.g. ina molecular weight range of the isolated lignin-derived components ofbetween 6.000 Da and 15.000 Da or 8.000 Da and 12.000 Da.

Ultra- and/or nanofiltration typically employ membranes, which arepreferably tubular membranes exposing solvent resistance, i.e. which arepreferably resistant at high and low pH values. Ultra- and/ornanofiltration is typically performed at elevated pressure, preferablyabove about 2 bar, more preferably at about 3 bar or above, even morepreferably at about 4 bar or above, most preferably at about 5 bar.Higher pressures may also be applied, e.g. above 10 bar, such as 10-15bar. Further, the applied temperature for the filtration step istypically higher than room temperature (25° C.) to facilitate isolationof the fraction of modified lignin-derived components. Usually, thetemperature is chosen such that degradation of the components to beisolated is essentially avoided. The temperature may be at least 40° C.,preferably at least 50° C., most preferably about 60-65° C.

Hence, the preferred membrane's cut-off size of the employed ultra- ornanofiltration in step (2) may depend on the expected molecular weightof the target modified lignin-derived components. For example, Kraftlignin being of a relatively small molecular weight may require amembrane cut-off of about 2 to kDa or from 2 to 8 kDa, while largerlignosulfonate may require a membrane cut-off of about 5 to 50 kDa oreven up to 100 kDa. Typically, the cut-off size for membranes to isolatelignosulfonate may be about 1 to 20 kDa.

If ultra- and/or nanofiltration is applied, it is preferably preceded bya pre-filtration step to separate larger debris, e.g. insoluble orpoorly soluble polymers and/or fragments thereof. Thereby, efficiencymay be increased as excessive blockade of the ultra- and/ornanofiltration membrane may be avoided, when isolating the fraction ofmodified lignin-derived components. Accordingly, the pre-filtertypically has a larger pore size and/or molecular weight cut-off thanthe ultra- and/or nanofiltration membrane.

Whether filtration is applied by step (2) or not may depend on whetherthe modified lignin-derived components are dissolved in the fluid phaseor suspended as solid components. Filtration is preferably used forseparation of suspended or dispersed solid, i.e. preferably dispersedparticles of a size of about >1 μm. By filtration, oversize solidparticles are typically retained by the membrane with the yielddepending on the character of the modified lignin components, theirparticle size and the filter's cut off.

Preferably, isolation step (2) thus comprises filtration and/orextraction, preferably ultrafiltration and/or nanofiltration by anultrafiltration and/or nanofiltration cell, preferably having apre-filtration section. Filtration in step (2) is preferably carried outin a ultrafiltration and/or nanofiltration cell comprising at least onemolecular weight cut-off unit, preferably at least two molecular weightcut-off units, wherein the at least one molecular weight cut-off unithas a cut-off level preferably of 0.5 kDa to 2 kDa.

(b) Extraction

Alternatively, extraction e.g. by means of an organic solvent, may beperformed. As used herein, “extraction” is typically a separationprocess comprising the separation of a desired substance from itsenvironment. It may include liquid-liquid extraction and/or solid phaseextraction. Extraction may use two immiscible phases to separatedissolved modified lignin-derived components from the original phaseinto another. By extraction, organic compounds are extracted by anorganic solvent from the aqueous phase. Common solvents for extractionare classified by their polarity from ethyl acetate (lowest polarity) towater (highest polarity): ethylacetate<acetone<ethanol<methanol<acetone:water (7:3)<ethanol:water(8:2)<methanol:water (8:2)<water, in the order of the Hildebrandsolubility parameter. The solution containing the extracted fraction(i.e. the components) may be dried, e.g. by using a centrifugalevaporator or a freeze-drier.

For example, Kraft lignin may be extracted by step (2) from the processstream, if less soluble in an aqueous medium than in appropriate organicsolvents (such as methanol, ethanol, acetone and aqueous mixturesthereof known in the art).

Alternative extraction techniques may include supercritical carbondioxide extraction, ultrasonic extraction, heat reflux extraction,microwave-assisted extraction, instant controlled pressure dropextraction (DIC), and perstraction. Amongst them, perstraction may bepreferred. Typically, “perstraction” includes two liquid phases, withonly one phase including a solvent for extraction. Perstraction mayadvantageously be more gentle, faster and cheaper than traditionalbiphasic extraction techniques. “Stripping” may be employed as anothergentle extraction alternative, which allows the fraction of modifiedlignin-derived components may be isolated from the process stream.“Stripping” is generally a physical separation process, wherein one ormore components are removed from a liquid stream by a vapor stream. Inindustrial applications, the liquid and vapor streams may be employedco-currently or flow countercurrent. Stripping is usually carried out ineither a packed or trayed column.

(c) Countercurrent Exchange

Isolation of the fraction of modified lignin-derived components in step(2) may generally be achieved by countercurrent flow, with the flowforwarded in opposite directions. For the inventive method theconcentration of dissolved modified lignin-derived components along theconcentration gradient may be envisaged. The counter-current exchangemethod may maintain the gradient of the two flows essentially stable forthe entire contact zone. Hence, countercurrent flow is particularlysuitable to isolate dissolved modified lignin-derived components and maybe less preferred for dispersed modified lignin-derived components.

(d) Precipitation

Further, precipitation may be employed as an isolation method to allow asolid fraction to be isolated from solution. Precipitation may also beemployed to control the amount of precipitated modified lignin (within agiven time window) by the choice of the added amount of precipitationagent and/or the pH. Preferably, precipitation according to step (2) (d)may be conducted by means of the addition of a cation, preferably a di-or multivalent cation, most preferably of calcium.

Precipitation according to step (2)(d) may be in particular preferredfor lignosulfonate or, equivalently, for sulfonated Kraft lignin.Precipitation by pH is less preferred, e.g. for lignosulfonate, as it isgenerally soluble in water over the entire pH range and may not bereadily isolated by pH modification. However, precipitation by calciumsalt addition may be preferred. E.g., excess lime (i.e. acalcium-containing inorganic material, in which carbonates, oxides andhydroxides typically predominate) may be added to the process stream,such that calcium lignosulfonate may precipitate. This process isgenerally known as Howard process. It is the most straight-forwardrecovery method known. Typically, up to 95% of the stream'slignosulfonate may be isolated by precipitation. Modified ligninresulting from the Kraft process (“Kraft lignin”) may be sulfonated instep (1) and thereafter subjected to, e.g., lime precipitation.

The remainder of modified lignin-derived components, which are notfurther employed by the present invention, may be channelled to thepaper manufacturing process or may serve for other applications such asenergy provision, or may be stored for later use or may be discarded.

Step (3): Chemical Decomposition

The isolated fraction of modified lignin-derived components of step (2)is subjected to chemical decomposition by step (3), wherein chemicaldecomposition step (3) may be carried out by (a) oxidative cracking ofthe modified lignin-derived components in the presence of a suitable(e.g. homogenous) catalyst comprising a metal or a metalloid component.Alternatively, chemical decomposition step (3) may be enabled (b) byreductive cracking of the modified lignin-derived components in thepresence of a suitable (e.g. heterogeneous) catalyst comprising a metalor a metalloid component. The terms “oxidative cracking” and “crackingand oxidizing” may be used interchangeably herein. The terms “reductivecracking” and “cracking and reducing” may be used interchangeablyherein. Alternatively, the modified lignin-derived components may besubjected to (c) electro-oxidation, preferably in alkaline or acidicsolution, or (d) to any other suitable decomposition method. The term“chemical decomposition” refers to the fact that the modifiedlignin-derived components are chemically decomposed, i.e. with regard totheir chemical structure. “Chemical decomposition” thus preferablydisrupts or alters chemical bonds, preferably covalent chemical bonds.

Any one of steps (3)(a)-(c) is envisaged to provide a lignin-derivedcomposition comprising at least one low molecular weight lignin-derivedcompound.

In step (3) of the inventive method, the isolated fraction of modifiedlignin-derived components of step (2) are subjected to a chemical (andoptionally physical) decomposition step. The reaction may allow toconvert the fraction of modified lignin-derived components of highermolecular weight to lower molecular weight compounds characterized bystructural elements or units of the initial lignin polymer. Step (3)corresponds to a decomposition reaction of the modified lignin-derivedcomponents resulting in a heterogeneous ensemble of preferably lowmolecular weight compounds of typically aromatic nature.

Disruption of the modified lignin-derived components into smallersubunits by chemical decomposition is an important step for ligninvalorization. The smaller subunits may preferably resemble the desiredtarget compounds, and may expose various functional groups on thearomatic rings to further catalytic transformation e.g. in step (6) ofthe inventive method.

“Chemical decomposition” is typically understood as the provision of aplurality of lower molecular weight compounds by chemical and/orphysical degradation of higher molecular weight starting material.Typically, such a reaction yields compounds comprising fragments ormoieties of the higher molecular weight starting material. Chemicaldecomposition may be studied by chemical analysis, e.g. by massspectrometry, gravimetric analysis, and thermogravimetric analysis.Preferably, decomposition according to the inventive method is carriedout by catalytic reaction, or alternatively, electrolytically. Thermaldecomposition may be employed as well according to the invention, but isless preferred, as it usually yields an even broader spectrum of diverselow molecular weight lignin-derived compounds. A larger fraction ofthese compounds following decomposition is of aromatic nature reflectingaromatic ring systems of the building blocks of the natural ligninpolymer provided in step (1).

Decomposition may result in a heterogeneous ensemble of lignin-derivedproducts comprising (modified) lignin-derived building blocks, i.e.“monomers” or “dimers”, preferably biphenylic dimers. Preferably, theresulting modified lignin-derived products herein essentially consist ofmonomers and dimers, i.e. the resulting lignin-derived products of step(2) do preferably not comprise larger (oligomeric) modifiedlignin-derived fragments but only modified lignin-derived monomers anddimers. Higher molecular weight modified lignin-derived componentsconverted by step (3), preferably chemically modified lignin polymers(such as lignosulfonate and Kraft lignin), decompose in a controllablemanner at elevated temperatures, preferably below the pyrolytictemperature of, e.g. 1000° C., such as at least 300° C., preferably atleast 400° C., more preferably 400 to 500° C. and in the presence of asuitable catalyst (e.g. in a oxidative cracking/reductive crackingreaction) and/or when subjected to electro-oxidation.

“Chemical decomposition” may comprise (alternative (a)) oxidativecracking of the modified lignin-derived components isolated in step (2).Typically, such decomposition is carried out in the presence of ahomogeneous metal ion-based or a metalloid-based catalyst. Byalternative (b), reductive cracking is applied to decompose the modifiedlignin-derived components in the presence of a heterogeneous metalion-based or metalloid-based catalyst. By alternative (c), said step ischaracterized by electro-oxidation of the modified lignin-derivedcomponents in alkaline or acidic solution.

“Cracking” is preferably a catalytic reaction to break or dissociatelarger molecules into their smaller fragments by dissociation ofcovalent bonds of the larger molecule. Generally, “cracking” describesany type of molecular dissociation under the influence of, e.g., heat,catalysts, electric currents and/or solvents.

Originally, the term “cracking” is typically used to refer to reactionsdeveloped for petrochemistry to disrupt larger e.g. gasoil moleculesinto smaller gasoline molecules and olefins. In that context, “cracking”makes use of a reactor and a regenerator for regenerating the catalyticmaterial. Therein, starting material may be injected into preferablyhot, fluidized catalysts. The resulting vapor-phase products may beseparated from the catalytic materials and fractionated into variousproduct or product fragment fractions by condensation. The catalyst istypically introduced into a regenerator, wherein air or oxygen ispreferably used to separate any residual components by an oxidationreaction, such that the surface of the catalyst is freed from anyby-products, which are formed as a result of the cracking process. Thehot regenerated catalyst may then be recycled to the reactor to completeits cycle. Isolated modified lignin-derived components derived from step(2) may be subjected to “cracking” conditions according to thisdefinition as well, although the term “cracking” is preferably andtypically to be understood as “oxidative cracking” or “reductivecracking” as defined above. “Cracking” of the isolated fraction modifiedlignin-derived components, e.g. Kraft lignin or lignosulfonates, istherefore preferably understood as the reaction underlying thedecomposition according to step (3) (a) or (b).

Cracking kinetics and the products of that reaction are typicallydependent on the temperature and/or the catalysts applied. In addition,the ensemble of products resulting from cracking is dependent on thenature of the lignin-derived fraction used as starting material for thedecomposition reaction. Accordingly, the fraction of modifiedlignin-derived components, e.g. Kraft lignin or lignosulfonate, may besubjected by step (3) to a catalytic reaction at a temperaturesignificantly lower than pyrolytic temperature or to electric current,preferably by electro-oxidation.

“Oxidation” is involved in the decomposition reaction according to step(3(a)). As used herein, “oxidation” refers to any reaction, whichincludes loss of electrons. More specifically, the term refers to theintroduction oxygen-containing functional groups, e.g. a hydroxyl group.For the method of the present invention, aromatic ring systems aretypically functionalized by an oxygen-containing functional group and/orby the substitution of a hydroxyl group by an oxo group. Oxidation istypically achieved by an oxidizing agent. An oxidizing agent may—moregenerally—correspond to any chemical species that removes electron(s)from another species. More specifically, it transfers (electronegative)oxygen to a substrate.

“Catalysis” is involved in step (3(a)) and (3(b)). It typically allowsto enhance the kinetics of a chemical reaction by the presence of acatalyst lowering the activation energy.

Preferred catalysts for oxidizing of the (modified) lignin-derivedcomponents in step (3(a)) are catalysts comprising metal ions, such assalts with catalytically active cations. Alternatively, (metal ormetalloid) coordination complexes may be employed. In general, a“coordination complex” is typically known in chemistry to consist of acentral atom, which may be a metallic or metalloid atom, e.g. a metalion or a metalloid ion. It is called the coordination center. Thesurrounding sphere of bound molecules or ions is known as ligands orcomplexing agents. Alternatively, catalysts may be of metalloidcharacter including coordination complexes, with a metalloid atom as thecoordination center, such as boron. In particular, catalysts usedaccording to step (3(a)) are homogeneous catalysts, but may also beheterogeneous catalysts. Generally, homogeneous catalysis is based oncatalytic reactions with the catalyst being in the same phase as thereactant(s). More specifically, a homogeneous catalyst is dissolved forcatalysis in the solution.

(a) Oxidative Cracking of Modified Lignin-Derived Components

Preferably, step (3) involves (a) oxidative cracking of the modifiedlignin-derived components.

Preferably, step (3(a)) may comprise oxidizing the modified ligninderived-components, preferably in the presence of a heterogeneous orhomogeneous catalyst or a combination of catalysts. Step (3(a)) istypically carried out in the presence of an oxidizing agent such as air,O₂ or H₂O₂ and preferably a catalyst or a mixture of catalysts, whichis/are preferably of heterogeneous nature, e.g. with regard to acracking reaction, but may also be of homogeneous nature.

Heterogenous catalysts of interest for step (3) (a) of the inventivemethod include TiO₂, Pt/TiO₂, Fe(III)/TiO₂, Pd/Al₂O₃, Ni/MgO, CH₃ReO₃,Cu—Ni, Cu-Mnm, Cu—Co—Mn, Cu—Fe—Mn, Cu—Ni—Ce/Al₂O₃, Cu—Mn/Al₂O₃.

Homogenous catalysts of interest for step (3) (a) of the inventivemethod may be selected from the following, non-limiting examples ofsuitable catalysts.

Homogenous catalysts applicable in step (3) (a) of the inventive methodmay include metalloporphyrins, including catalysts formed from themetalation of the porphyrin with transition metal salts.Metalloporphyrins of interest as catalysts in step (3)(a) of theinventive method include Mn(TSPc)Cl, Fe(TSPc)Cl, Fe(TF₅PP)Cl, CoTSPc,FeTSPc, Rh(TSPP), Fe(TF₅PP)Cl and Mn(TSPP)Cl. Crestini and Tagliatestaprovide an extensive review on the oxidation of lignin usingmetalloporphyrin complexes (cf. Crestini and Tagliatesta. The PorphyrinHandbook; Kadish, K. M., Smith, K. M., Guilard, R. Eds.; Academic Press:San Diego, Calif., 2003; Vol. 11, p 161).

Homogenous catalysts applicable in step (3)(a) of the inventive methodinclude Schiff-base catalysts, especially metallosalen catalysts. Theseare emerging as promising oxidation catalysts of lignin and modifiedlignin-derived components. The term “salen” refers to[N,N′bis(salicylidene)ethane-1,2-diaminato]. Metallosalen catalysts ofinterest as catalysts in step (3)(a) of the inventive method includeCo(salen), [(pyr}Co(salen)], Cu-, Fe-, andMn-triphenylphosphonium-decorated salen complexes, Co-sulphosalen,Co(salen)/SBA-15, and [Co(N-Me salpr)].

Homogenous catalysts applicable in step (3)(a) of the inventive methodinclude nonporphyrinic or Schiff base catalysts, including metallo-TAML(tetraamido macrocyclic ligand), -DTNE(1,2-bis-(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethane) and -TACN(1,4,7,-trimethyl-1,4,7-triazacyclononane) catalysts. The metal may forinstance be selected from iron or manganese. Catalysts of use in step(3)(a) of the inventive method in this regard include Mn(IV)-Me₄DTNE andMn(IV)-Me₄TACN.

Homogenous catalysts applicable in step (3)(a) of the inventive methodinclude polyoxometalates (POMs), as reviewed in detail by Gaspar et al.Green Chem. 2007, 9, 717. Polyoxometalates consist of both primary andsecondary heteroatoms, where the former typically determines thestructure and the latter, typically transition metal ions, may besubstituted without change of structure. Thereby, secondary heteroatomscan be replaced by ions conferring desirable redox characteristics. POMsof interest as catalysts in step (3)(a) of the inventive method includeSiW₁₁Mn(III), BW₁₁Co(III), PW₁₁Ru(IV), heteropolyanion-5-Mn(II),alpha-[SiVW₁₀O₄₀]⁵⁻, Na_(5(+1.9))[SiV_(1(−00.1))MoW_(10(+0.1))], LaMnO₃,LaCoO₃, H₂MoO₄ and Fe₂(MoO₄)₃. POMs may be utilized as catalysts inconjunction of O₂ or H₂O₂ as oxidants.

Homogenous catalysts applicable in step (3)(a) of the inventive methodinclude simple metal salt-based catalysts. These may typically utilizedin conjunction with O₂ as oxidant. Metal salt-based catalysts ofinterest as catalysts in step (3)(a) of the inventive method includeCo(OAc)₂/Mn(OAc)₂, Co(OAc)₂/Mn(OAc)₂/HBr, Co(OAc)₂/Zr(OAc)₄/HBr,Mn(OAc)₂, CuSO₄, CuSO₄/FeCl₃, Cu(OH)₂, FeCl₃, Fe₂O₃, NaBr2,2,6,6-tetramethylpiperidine-1-oxyl-radical (TEMPO), CuO, and CoO.

Homogenous catalysts applicable in step (3)(a) of the inventive methodfurther include miscellaneous catalysts, includinghexacyanoruthenate(II)), Ru/CN)₆ ⁴⁺,tris-(4,4′-dimethyl-2,2′-bipyridine)iron(II) and [Cu(phen)(OH)₂].

In principle, step (3)(a) of the inventive method can be performed withany of the aforementioned homogenous catalysts.

Preferably, the employed catalyst may comprise a metal ion, preferablyselected from Co(II), Cu(II), Fe(II) and Fe(III), more preferablyFe(III). Alternatively, the catalyst may comprise a metalloid element.The “metalloid element” and/or the metal ion is/are preferably providedas coordination complex or, alternatively, as a salt. In such acoordination complex, a metalloid element or metal ion forms thecoordination center. Typically, a “metalloid” is a chemical element withmetallic and non-metallic properties. Metalloid may be any elementselected from boron, silicon, germanium, arsenic, antimony, tellurium,aluminum, and selenium. A metalloid may have a metallic appearance, itis typically brittle and only a fair conductor of electricity.Chemically, it may behave mostly like a non-metal. Metalloid comprisingagents are particularly useful as catalysts. Preferably, the metalloidcatalyst comprises the metalloids B(III), Si(IV) and/or Al(III). Themetalloid catalyst may preferably be a boron catalyst, comprisingpreferably B(III). As an example: When using a boron catalyst, step (3(a)) may be a hydroboration-oxidation reaction, which is preferably atwo-step organic reaction. It converts, e.g., an alkene into a neutralalcohol by the net addition of water to the double bond. The hydrogenand hydroxyl group are preferably added in syn addition providing analcohol in cis stereochemistry. Hydroboration-oxidation typicallyreflects an anti-Markovnikov reaction, with the hydroxyl group beingattached to the less-substituted carbon.

More preferably, the homogeneous catalyst in step (3(a)) is selectedfrom the group consisting of a salt, a coordination complex, a zeolite,a polyoxometalate, and a combination of any of them. Any such catalystspreferably comprises a metal ion selected from Co(II), Cu(II), Fe(II)and Fe(III), most preferably Fe(III).

(Synthetic) zeolites are typically microporous, aluminosilicateminerals, which are known as adsorbents and catalysts. Zeolites arewidely used as catalysts in the petrochemical industry, for instance influid catalytic cracking and hydrocracking. Zeolites may also be used asactive catalytic solid-state acids in applications other than inpetrochemistry. Hence, zeolites may facilitate numerous acid-catalyzedreactions, as they may be foreseen for the present invention. They maybe employed as catalysts for the oxidative cracking reaction e.g. ofstep (3(a)) of the present inventive method.

Catalysts reflecting polyoxometalate(s) (POM(s)) are polyatomic ions,usually anions that may be composed of three or more transition metaloxyanions, which are linked together by shared oxygen atoms to form aclosed 3-dimensional framework. POMs may advantageously be employed foroxidation of organic compounds, in particular for oxidation of thefraction of modified lignin-derived components isolated in step (2).

It is preferred that oxidative cracking according to step (3(a)) may beperformed in the presence of a metal catalyst, in particular a Cu(II) orFe(III) containing catalyst. Alternatively, a Co(II) comprising catalystmay be employed. The catalyst is preferably a heterogeneous catalyst,but may also be a homogeneous catalyst. The metal catalyst, inparticular the Cu(II) or Fe (III) containing catalyst, is preferably a(metal or metalloid) salt. The oxidative cracking reaction is preferablycarried out under elevated temperature and/or pressure conditions.

The reaction of step (3(a)) may be carried out at a temperature of 30 to400° C., preferably 100 to 350° C. The temperature chosen for thatreaction is selected such that it is significantly lower than pyrolytictemperatures, e.g. lower than 1000° C. or 800° C. or lower than 500° C.By such a lower temperature reaction, the reaction products aretypically less diverse than by a purely pyrolytic reaction (or pyrolyticdecomposition).

For example, the solution comprising the fraction of modifiedlignin-derived components of step (2), e.g. lignosulfonate, is madealkaline, preferably by adjusting the pH value to at least 9. The mediummay preferably also be acidic. The metal and/or metalloid catalyst, inparticular the Fe(III) containing catalyst, may be added thereafter tothat solution. Said catalyst comprising solution may be heated to atemperature of at least 150° C., preferable to a temperature of 150 to300° C., more preferably 160-170° C. The pressure may be set to anoverpressure of at least 5 atm, preferably from 10 to 12 atm. Whenapplying such temperature and pressure conditions, cracking occurs andoxidizing may typically take place simultaneously due to the air'soxygen as oxidizing agent.

In contrast to employing air as oxidizing agent, step (3(a)) employing ametal and/or metalloid catalyst, in particular the Fe(III) containingcatalyst, may be conducted in an oxygen enriched environment, morepreferably under increased pressure, in particular increased oxygenpartial pressure. Said pressure may—preferably under alkalineconditions—be at least 3 bar p(O₂), more preferably 4 to 5 bar p(O₂).Under acidic conditions, the p(O₂) may advantageously be at least 10bar, sometimes at least 20 bar. Further advantageously, an alcohol,preferably methanol, may be added to the reaction to avoidre-polymerisation of the lignin-derived components.

The alcohol may be added in an amount of at least 5%, preferably atleast 10%, more preferably at least 20%, even more preferably at least30%, even more preferably at least 40%, even more preferably at least50%, even more preferably at least 60%, even more preferably at least70%, most preferably at least 80% with respect to the total reactionvolume.

The alcohol, in particular methanol, may be recovered before or afterisolation/purification of the target compound in step (4) of theinventive method. In the recovery step, the alcoholic ingredient, inparticular methanol, is preferably recovered by heating andvaporization. The recovery step is preferably performed after isolationstep (4) of the inventive method.

Oxidative cracking is preferably carried out in a single reactionvessel, preferably simultaneously. The temperature is preferably atleast 150° C., more preferably at least 170° C. The reaction may becarried out in solution under constant stirring, e.g. above 500, 600,700, 800, 900 or 1.000 rpm. Said oxidation in the presence of an oxygenenvironment may be performed in a fluidized bed reactor, particularly areactor comprising a sand bed. Under such conditions, the temperaturemay be set to at least 250° C., preferably to at least 300° C. Thereby,the oxidation rate may advantageously be increased. Upon application ofa fluidized bed reactor, less desired or undesired by-products otherthan the target aromatic or phenolic compounds are preferably lessfrequently observed, which is preferred for step (3) of the inventivemethod.

In accordance with the above, step (3) (a) oxidative cracking of themodified lignin-derived components is preferably carried out in thepresence of an oxidizing agent and a heterogeneous or homogeneouscatalyst comprising (a) a metal ion selected from Co(II), Cu(II), Fe(II)and Fe(III); or (b) a metalloid component selected from B(III), Si(IV)and Al(III) preferably at a temperature of 30-400° C., more preferably100-350° C. Preferred homogenous catalysts employed in step (3)(a)include those selected from the group consisting of a salt, acoordination complex, a zeolite and a polyoxometalate comprising a metalion selected from Co(II), Cu(II), Fe(II) and Fe(III).

(b) Reductive Cracking of Modified Lignin-Derived Components

In the alternative, decomposition in step (3) may be carried out byreductive cracking the fraction of modified lignin-derived componentsisolated in step (2), which is typically conduted in the presence of areducing agent (alternative (b)) and a suitable catalyst. By alternativestep (3(b)), the fraction of modified lignin-derived components istherefore reduced, typically by addition of a reducing agent. A“reducing agent” is understood as an agent which “donates” electron(s)to another chemical species (electron donor).

The reducing agent is preferably hydrogen or an alcohol as H-donor. Sucha reaction under reducing conditions typically also requires a suitablecatalyst.

Heterogenous catalysts applicable for reductive cracking according tostep (3)(b) of the inventive method include, without limitation, Cu—CrO,Raney Ni, Rh, Pd. FeS, Co—Mo, Ni—Mo, Co—Mo—P, Fe₂O₃, Mo, Ni—Mo—P, Mo₂N,Ni—W, Rh—Co, Ni—Cu, NiO—MoO₃, MoO₃Ru, M or M—Mo (wherein M is selectedfrom Co, Cu, Ir, Ru, Pd, Fe, Rh, Pt or Ni). Optionally, the support(i.e. a material to which the catalyst is affixed) may be selected fromcarbon, A12O₃, TiO₂, SiO₂—Al₂O₃, ZrO₂, CeO₂, zeolite, MgO or nothing.

A homogeneous catalyst may, however, alternatively be employed in step(3)(b) of the inventive method. Suitable homogenous catalysts include(1,5-hexadiene)RhCl dimer, colloidal rhodium, [(1,5-C₆H₁₀)RhCl]₂,rhodium nanoparticles, [(C₆H₆)Ru₄H_(4])]Cl₂, [(Ru(C₅H₅)Cl(TPPDS)₂],NaBH₄+I₂, and RuCl₂(PPh₃)₃.

Preferably, a heterogeneous catalyst comprising, e.g., a metal selectedfrom nickel, platinum, palladium, ruthenium, rhenium and gold may beemployed. The catalyst is preferably provided on the surface of asupport material preferably selected from the group consisting of activecarbon, silica, titaniumoxide and/or aluminumoxide. Thereby, thelignin-derived components may be subject to e.g. hydrogen based “lysis”by cleavage of carbon-carbon or carbon-heteroatom single bonds(hydrogenolysis).

The catalyst typically employed by step (3(b)) is a heterogeneouscatalyst, which is defined as a catalyst provided in another phase,typically in solid or gaseous phase, than the reactant(s), which aretypically provided in solution. A homogeneous catalyst may, however,alternatively be employed. For the present method, the modifiedlignin-derived components are typically provided in solution and thecatalyst is usually provided as solid matter. Generally, heterogeneouscatalysis provides the advantage that reaction products may readily beseparated from the catalyst component. Advantageously, heterogeneouscatalysts are usually more stable and decompose more slowly thanhomogeneous catalysts. They may be recycled.

For example, reductive cracking of the fraction of modifiedlignin-derived components isolated in step (2) may be carried out bymeans of a catalyst comprising nickel, e.g. supported on activatedcarbon (Ni/C). Therein, a fragmentation-hydrogenolysis process of themodified lignin into lower molecular weight lignin-derived targetcompounds, e.g. di- or monomeric phenolic target compounds, in alcoholicsolvents over nickel-based catalysts may be performed. This reactioninvolves hydrogenolysis of modified lignin components into di- ormonomeric phenolic compounds over nickel catalysts, wherein alcohol ispreferably the source of active hydrogen as the reducing agent.

In an alternative example, the fraction of modified lignin-derivedcomponents from step (2) may be preferably cracked and reduced in thepresence of Ruthenium deposited on a carbon catalyst (Ru/C) inpreferably an organic solvent, such as methanol, under a reducingatmosphere, such as an H₂ atmosphere, preferably at elevatedtemperatures. Such a reaction preferably provides, other than residualcarbohydrate pulp, lignin oil. The resulting phenol-rich lignin oiltypically consist more than 50% (w/w) of phenolic monomers as targetcompounds of the present invention (mainly) and 10% to 25%, preferablyless than 20% (w/w) of phenolic dimers. The obtainable target compoundsby that reaction (or alternative reactions) are one or more of syringol,in particular 4-n-propylsyringol, 4-ethylphenol, and guaiacol, inparticular 4-ethylguaiacol and 4-n-propylguaiacol.

Alternatively, steps (1) (degradation) and (3) (decomposition) may becombined, which does preferably not require step (2). The combineddegradation/decomposition reaction (steps (1) and (3) combined) mode ofthe inventive method may preferably, but not necessarily be carried outby employing step (3(b)) according to the inventive method. Therein, thenatural lignocellulosic material provided in step (1) may be delignifiedthrough simultaneous solvolysis and catalytic hydrogenolysis of thelignin material in one single step. Combined solvolysis and catalytichydrogenolysis may preferably be carried out in the presence ofRuthenium preferably deposited on a carbon catalyst (Ru/C), preferablyin an organic solvent, such as methanol, under a reducing atmosphere,such as an H₂ atmosphere. The reaction is preferably carried out atelevated temperatures. The resulting product of combined solvolysis andcatalytic hydrogenolysis may be further processed as described herein toobtain a purified fraction of low molecular weight aromaticlignin-derived (mono- or dimeric) compounds.

In accordance with the above, step (3) (b) reductive cracking of themodified lignin-derived components is preferably carried out in thepresence of a reducing agent, preferably hydrogen or a hydrogen donatingalcohol, and a heterogeneous catalyst comprising a metal selected fromnickel, platinum, palladium, ruthenium, rhenium and gold, preferablyprovided on the surface of a support material, preferably selected fromthe group consisting of active carbon, silica, titaniumoxide andaluminumoxide.

Further advantageously, an alcohol, preferably methanol, may be added tothe reaction to avoid re-polymerisation of the lignin-derivedcomponents.

(c) Electro-Oxidation of Modified Lignin-Derived Components

Finally, decomposition in step (3) may be carried out byelectro-oxidation (alternative (c)).

With regard to step (3)(c), “electro-oxidation” is understood asoxidation at the surface of an electrode and/or in an electrical(electrochemical) cell. Specifically, “electro-oxidation” is defined asan electrochemical process, wherein the oxidation reaction occurs byapplying an electric field between two electrodes, e.g. a workingelectrode and a counter electrode, for the oxidation reaction to takeplace. Preferably, any such electrical cell employed by step (3(c) is asingle galvanic cell or a flow cell. A flow cell is characterized by theionic solution (electrolyte) passing continuously or batch-wise throughthe cell. The ionic solution is typically stored in separate storagetanks.

The “working electrode” (electrode in an electrochemical system, onwhich the reaction of interest takes place) is cathodic or anodic,respectively, depending on whether the reaction on the electrode isreduction or oxidation. Common working electrodes may comprise inertmetals, such as gold, silver or platinum, or inert carbon, such asglassy carbon or pyrolytic carbon, or mercury drop and film electrodes.The working electrode employed by the present invention mayalternatively also be a nickel or nickel alloy electrode. The counterelectrode may be a platinum electrode, in particular whenever theworking electrode is a nickel electrode. The electrodes may be, forexample, sintered electrodes, which preferably benefit from extendedlife time and show a higher oxidation capacity than other technologies.Electro-oxidation may be advantageous, as it provides instant operationon demand (“on/off”). Further, no aggressive chemicals are required, andreaction temperatures may be kept low. As the large diversity ofby-products is avoided, it allows to efficiently produce lower molecularweight aromatic lignin-derived target compounds. As compared to thermaldecomposition methods, energy consumption is reduced.

The electro-oxidation reaction may preferably performed in strongalkaline solution of at least pH 10, and preferably, constant current isapplied. Preferred is electro-oxidation carried out galvanostatically atpH 10 to 14. Preferably, the solution comprising the modifiedlignin-derived components, e.g. lignosulfonate, acts as anolyte and,typically, NaOH solution as catholyte. In general, an anolyte is thepart of the electrolyte, which is under direct influence of the anodeupon electrolysis. Correspondingly, a catholyte is the part of theelectrolyte, which is under direct influence of the cathode uponelectrolysis. Alternatively, electro-oxidation may preferably also becarried out under acidic conditions. Further, the modifiedlignin-derived components in solution may serve as anolyte and catholyteat the same time. Advantageously, no (semi-permeable) membrane isrequired for the inventive method. In terms of the electrolyte, nospecific electrolyte is required, if the reaction is carried out inacidic or alkaline medium.

Alternatively or additionally, a salt or distinct salts, preferably analkali salt, may be added to the electrolyte, e.g. a sodium salt,preferably sodium sulfate.

In accordance with the above, step (3) alternative (c) electrooxidationis preferably carried out galvanostatically, preferably at a pH from pH1 to 14.

Electro-oxidation may also directly yield the target compounds (e.g.quinones). In such cases, the isolation/purification step (4) may beomitted.

(d) Other Methods

Chemical decomposition in step (3) of the inventive method may also beaccomplished using other methods as described herein.

Enzymatic decomposition according to step (3) (d) of the inventivemethod may be accomplished by contacting the modified lignin-derivedcomponents with suitable enzymes (or organisms producing the same, inparticular fungi) under appropriate conditions. Enzymes of interest inthis regard include inter alia oxidases, peroxidases and hydrolyticenzymes, e.g. derived from Phaerochaete chrososporium or Pycnoporuscinnabarinus.

Photooxidation according to step (3) alternative (d) may involvesubjecting the modified lignin-derived components to visible or UVlight, typically with a wavelength of up to 500 nm.

Alternatively, step (3)(d) of the inventive method may comprise chemicaldecomposition in ionic liquids. Ionic liquids are composed of ionicorganic/inorganic salts that are liquid at low temperature (<100° C.).They typically have low vapour pressures, are chemically and thermallystable and are able to dissolve in a wide range of compounds. Variousdecomposition reactions can be carried out in ionic liquids, forinstance acetylation, acid hydrolysis, heat treatment, acylation ofenzymatic treatment as described above. Ionic liquids of interest forthe decomposition of the lignin-derived components of the inventioninclude those comprising alkylsulfonates, lactates, acetates, chloridesor phosphates as anions. One of the most important advantages of someionic liquids (e.g. 1-H-3-Methylimidazolium chloride,1-ethyl-3-imidazolium chloride) is their ability to act as both anacidic catalyst and a solvent. Such ionic liquids may be particularlypreferred. Ionic liquids may be used in conjunction with suitabletransition metal catalysts (e.g. 1-ethyl-3-methylimidazoliumdiethylphosphate and COCl₂ □ 6 H₂O, 1-ethyl-3-methylimidazoliumtrifluoromethylsulfonate and Mn(NO₃)₂) which may promote thedecomposition of modified lignin-derived components.

Optionally, the above-mentioned alternatives may be combined with eachother. E.g., a synergistic combination of photo-electrocatalysis using athree-electrode iridium oxide system coupled with UV light may beemployed. A combination of enzyme-based approaches and ionic liquid isdescribed above.

Step (4): Isolation and Optional Modification and Purification ofPrecursor Compounds

Finally, in step (4), the lmw (aromatic) lignin-derived precursorcompounds provided by the chemical decomposition step (3) is subjectedto an isolation step (sub-step (4.1)). As indicated above, any of themethods according to (3)(a)-(c) (or (d)) can be employed for chemicaldecomposition of the modified starting materials. Chemical decompositionaccording to (3)(a)-(c) preferably yields lmw (aromatic) lignin-derivedprecursor compounds that are purified in step (4) of the inventivemethod.

Hereby, the lignin-derived lmw (aromatic) precursor compounds mayisolated from, e.g., higher molecular weight aromatic lignin componentsand/or preferably from other non-lignin-derived residual components,including e.g. inorganic reactive agents. In step (4), the desiredlignin-derived precursor compounds are thus separated from (residual)higher molecular weight aromatic lignin-derived components and/or othernon-lignin-derived residual components, which have not been decomposedor decomposed to a less significant degree, or which have adverselyre-polymerized (sub-step (4.1)). The lmw aromatic lignin-derivedcompounds may further be subjected to annulation reactions (sub-step(4.2)), oxidation reactions (sub-step (4.3)) and one or morepurification step(s) (sub-step (4.4)), and/or derivatization reactions(sub-step (4.5)) wherein sub-steps (4.1) to (4.5) may be performed inany suitable order.

Thereby, step (4) yields the precursor compounds that are subsequentlymodified to yield the sulfonated redox active target compoundsparticularly envisaged for use as redox flow battery electrolytes.

The obtained precursor compounds may optionally further be subjected toannulation and/or oxidation reactions, before being modified in step (5)of the inventive method.

Precursor Compounds

The lignin-derived lmw (aromatic) precursor compounds isolated in step(4.1) of the inventive method are preferably monomers comprising one(typically monocyclic) aromatic ring system or dimers comprisingtypically two (non-annulated, typically monocyclic) aromatic rings,which may preferably be linked by a linker moiety, preferably analiphatic linker, or by a bond. The precursor compounds obtained in step(4) of the inventive method thus preferably qualify as “aromatic”compounds.

The term “aromatic” refers to a compound, which fulfils the criterion ofaromaticity—as it is generally defined in the art. Therein, the term“aromatic” is typically used to describe a cyclic, i.e. ring-shaped, andplanar system that exhibits increased stability as compared to linear,i.e. line-shaped, molecules with the same number of atoms. As a resultof its increased stability, the aromatic system is less prone to reactunder conventional conditions. In terms of the electronic nature of themolecule, aromaticity describes a conjugated system usually described byalternating single and double bonds within the ring system. Thisconfiguration typically allows for the electrons in the molecule's pisystem to be delocalized around the ring, increasing the molecules'stability. The most commonly encountered aromatic system in organicchemistry are benzene and its derivatives. The model description forbenzene typically consists of two resonance forms, which corresponds tothe double and single bonds superimposing to produce six one-and-a-halfbonds. Benzene is more stable by its charge delocalization than is to beexpected. Non-carbocyclic and/or non-hexacyclic aromatic systemsunderstood to be aromatic as well, if they fulfil the aromaticity rules,such as heterocyclic aromatic compounds, di- tri- and tetracycliccompounds and compounds having any n-membered rings such as 5-memberedrings. Any aromatic functional group may be designated as “aryl group”.Aromatic compounds are commonly isolated in the art from petroleum orits refined fractions.

A lignin-derived lmw (aromatic) precursor compound envisaged to beisolated by step (4) typically exhibits a molecular weight of less than1.000 Da, preferably less than 700 Da, more preferably less than 500 Da,most preferably of about 100 to 500 Da, e.g. 200 to 400 Da. It typicallyhas a size in the order of 10⁻⁹ m or less. Preferably, such a precursorcompound is based on a monomer or, alternatively, a homo- or heterodimerof the polymeric natural lignin, which may have been modified in thepulping process of step (1.2) of the inventive method. “Monomers”essentially correspond to the (repetitive) building blocks of polymericnatural lignin. A “monomer” may be any building block of the naturallignin polymer, which may be modified in step (1) . “Monomers” of thenatural lignin polymer are typically of aromatic nature (e.g. contain anaromatic ring system), but may be diverse in terms of their specificchemical character.

Typically, precursor compounds are monocyclic phenolic derivatives orencompass two such monomeric moieties each containing individual(non-annulated) phenolic ring systems, respectively. Specifically, theprecursor compound may comprise one single benzene-derived (substituted)aromatic ring system.

For a dimeric precursor compound, the ring systems may be directlyconnected by a bond. Alternatively, two monomeric moieties containing anaromatic ring system each may be connected by a linker group, e.g. analiphatic linker group, to form a homo- or heterodimer, typically aheterodimer. A heterodimer exhibits two aromatic ring systems withindividual (distinct) substitution patterns. It may be preferred for thedimer to represent the basic chemical structure of two (substituted)aromatic ring systems directly linked by a bond to form a biphenylicring system. Precursor compounds comprising two aromatic ring systemsmay thus preferably form a biphenylic moiety. Preferably, the one ormore carbocyclic ring(s) of the precursor compounds may be carbocyclic.Precursor compounds obtained by the inventive method may thus comprisecarbocyclic benzene or its benzene derivatives, such as phenolicderivatives. While compounds essentially comprising benzene-derivedaromatic ring systems and its derivatives are preferred, aromaticprecursor compounds comprising biphenylic, bi- and multicyclic(annulated) aromatic systems may likewise be envisaged.

The aromatic ring(s) of the lignin-derived precursor compound is/arepreferably substituted in at least one, preferably in at least twopositions by a functional group, wherein the at least one functionalgroup is preferably alkoxy or hydroxyl. Therein, a monocyclic precursorcompound is typically substituted in at least two positions by afunctional group, wherein the functional group is preferably alkoxy orhydroxyl. A precursor compound having two ring systems, in particular abiphenylic compound, is typically substituted in at least one positionper aromatic ring by a functional group. Preferably, each ring systemexhibits its individual substitution pattern being different from theother substitution pattern of the other ring system. Preferably, the atleast one functional group is alkoxy or hydroxyl.

Specifically, the at least one lignin-derived lmw aromatic precursorcompound may be characterized by general Formula (Ia):

wherein

-   -   each of R¹-R⁵ is independently selected from hydrogen, hydroxy,        carboxy, linear or branched, optionally substituted, C₁₋₆ alkyl,        linear or branched, optionally substituted, C₁₋₆ alkenyl, linear        or branched, optionally substituted, C₁₋₆ alcohol, linear or        branched, optionally substituted, C₁₋₆ aminoalkyl, linear or        branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or        branched, optionally substituted, C₁₋₆ alkoxy, linear or        branched, optionally substituted, C₁₋₆ aldehyde, ester, oxo or        carbonyl; and    -   R⁶ is selected from the group consisting of hydrogen, hydroxy,        linear or branched, optionally substituted, C₁₋₆ carboxyl,        linear or branched, optionally substituted, C₁₋₆ aldehyde, and        linear or branched, optionally substituted, C₁₋₆ alcohol.

Alternatively, the at least one lignin-derived lmw aromatic precursorcompound may be characterized by general Formula (Ib):

-   -   each of R¹-R⁹ is independently selected from hydrogen, hydroxy,        carboxy, linear or branched, optionally substituted, C₁₋₆ alkyl,        linear or branched, optionally substituted, C₁₋₆ alkenyl, linear        or branched, optionally substituted, C₁₋₆ alcohol, linear or        branched, optionally substituted, C₁₋₆ aminoalkyl, linear or        branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or        branched, optionally substituted, C₁₋₆ alkoxy, linear or        branched, optionally substituted, C₁₋₆ aldehyde, ester, oxo or        carbonyl; wherein R⁵ is preferably hydroxy or optionally        substituted C₁₋₆ alkoxy; and    -   R¹⁰ is selected from the group consisting of hydrogen, hydroxy,        linear or branched, optionally substituted, C₁₋₆ carboxyl,        linear or branched, optionally substituted, C₁₋₆ aldehyde, and        linear or branched, optionally substituted, C₁₋₆ alcohol.

Alternatively, the at least one lignin-derived lmw aromatic precursorcompound may be characterized by general Formula (Ia):

wherein

-   -   each of R¹-R⁵ is independently selected from H, optionally        substituted C₁₋₆ alkyl, optionally substituted C₁₋₆ alkenyl,        halogen, optionally substituted C₁₋₆ alkoxy, amino, nitro,        phosphoryl, and phosphonyl; wherein at least one of R¹, R³ or R⁵        is hydroxy or optionally substituted C₁₋₆ alkoxy; and    -   R⁶ is selected from the group consisting of hydrogen, hydroxy,        linear or branched C₁₋₆ carboxyl, linear or branched C₁₋₆        aldehyde, and linear or branched C₁₋₆ alcohol,

or by general Formula (Ib):

-   -   each of R¹-R⁹ is independently selected from H, optionally        substituted C₁₋₆ alkyl, optionally substituted C₁₋₆ alkenyl,        halogen, optionally substituted C₁₋₆ alkoxy, amino, nitro,        phosphoryl, and phosphonyl; wherein R⁵ is preferably hydroxy or        optionally substituted C₁₋₆ alkoxy; and    -   R¹⁰ is selected from the group consisting of hydrogen, hydroxy,        linear or branched C₁₋₆ carboxyl, linear or branched C₁₋₆        aldehyde, and linear or branched C₁₋₆ alcohol.

As used herein, “Hydrogen” is H. “Hydroxy” or “Hydroxyl” is —OH.“Carboxy” or “carboxyl” is preferably —COOH. An exemplary ion of carboxyis —COO—. The term “alkyl” refers to a saturated aliphatic groups,including linear (straight-chain) and branched alkyl groups, cycloalkyl(alicyclic) groups, alkyl substituted cycloalkyl groups, and cycloalkylsubstituted alkyl groups. The term “alkenyl” refers to unsaturatedaliphatic groups analogous in length and possible substitution to thealkyls described above, but that contain at least one C—C double bound.The term “alkoxy” or “alkoxyl” refer to an alkyl group, as definedabove, having an oxygen radical attached thereto. Representative alkoxylgroups include methoxy, ethoxy, propyloxy, tert-butoxy and the like.“Alkoxy” thus preferably refers to a group of formula —OR, wherein R ispreferably an alkyl group, as defined herein. The term “aldehyde” refersto a group of formula —RCHO, wherein R is preferably selected from H oran alkyl group as defined above. “Halogen” is fluoro, chloro, bromo, oriodo. The terms “amine” and “amino” refer to both unsubstituted andsubstituted amines, i.e. groups of formula —NR¹R¹R³, wherein R¹, R² andR³ are independently selected from H and an alkyl group or anotherfunctional group. The term includes “amino” (—NH₂). An exemplary ion ofamino is —NH₃+. The term further includes primary amines, wherein one ofR¹, R² and R³ is an alkyl group or other functional group. The termfurther includes secondary amines, wherein two R¹, R² and R³ areindependently selected from an alkyl group or other functional group.The term further includes tertiary amines, wherein all of R¹, R² and R³are independently selected from an alkyl group or other functionalgroup. The term “amide” refers to a group of formula —RC(O)NR¹R²,wherein R¹ and R² are independently selected from H, alkyl, or alkenyl.“Nitro” is —NO₂. “Oxo” is ═O. The term “carbonyl” refers to a group ofthe formula —R¹C(O)R², wherein R¹ and R² are independently selected fromnothing, a bond, H, O, S, alkyl, or alkenyl. “Phosphoryl” is —PO₃H₂.Exemplary ions of phosphoryl are —PO₃H⁻ and —PO₃ ²⁻. “Phosphonyl” is—PO₃R₂, wherein each R is independent H or alkyl, as defined herein. Anexemplary ion of phosphoryl is —PO₃K. “Cyanide” is —CN. “Sulfonyl” is—SO₃H. An exemplary ion of sulfonyl is —SO₃—.

Preferably, the at least one lignin-derived lmw aromatic precursorcompound is selected from the group consisting of phenolic derivativesof biphenyl, benzylalcohol, benzalde-hydes and benzoic acid, preferablyderivatives of p-hydroxy benzylalcohol, p-hydroxy benzaldehydes andp-hydroxy benzoic acid, or more preferably vanillin, guaiacol, eugenol,syringol, phenol, syringaldehyde, and/or a derivative of any of theabove, and/or a combination of the above.

Preferred are lignin-derived precursor compounds, which are representedby the following structures and corresponding esters:

Monomeric lignin-derived precursor compounds containing one aromaticring are typically derived from a monomer of the modified lignin-derivedcomponent. Dimeric lignin-derived precursor compounds containing twoaromatic rings, which form a biphenylic system, are obtainable bychoosing the appropriate lignocellulosic starting material, whichencompasses such moieties, e.g. from spruce. Such a biphenylic systemtypically comprises phenylbenzene or 1,1′-biphenyl as essential chemicalstructure. Biphenylic moieties are typically formed by 5-5-linkage ofnatural lignin monomers. Such a bond occurs more frequently in softwoodthan in hardwood. For example, spruce may comprise more than 15%,preferably more than 20%, even more preferred more than 25% biphenylicmoieties among its phenyl-propane units making up its natural lignin.Whenever biphenylic precursor compounds are envisaged, it may bepreferred to use spruce wood as a lignocellulosic starting material instep (1) of the inventive method. Biphenylic precursor compounds may befurther processed by chemical reactions, e.g. in further oxidizingreactions, in order to provide e.g. redox active compounds for multiplebeneficial uses.

Sub-Step (4.1) Isolation of Precursor Compositions and - Compounds

Isolation sub-step (4.1) of the inventive method is another isolationstep, which may preferably comprise subjecting the product obtained fromchemical decomposition step (3) to filtration and/or extraction,preferably filtration, to obtain lignin-derived lmw (aromatic) precursorcompounds as defined above (or compositions comprising or (essentially)consisting thereof). Said precursor compounds are isolated in sub-step(4.1) from other components resulting from decomposition of step (3),e.g. fragments other than the monomeric or dimeric precursor compounds,by appropriate techniques.

“Fragments” of the modified lignin-derived components are typicallylarger in molecular weight than the monomeric or dimeric precursorcompounds, but have typically a lower molecular weight than the modifiedlignin-derived components obtained by step (2) of the inventive method.Such fragments are typically not understood to be precursor compounds ofthe inventive method. Instead, they may comprise or they are tri- orn-mers of the building blocks of the modified lignin-derived components.Such fragments resulting from the decomposition step are typicallyoligomers being of smaller molecular weight than the modifiedlignin-derived components obtainable in the pulping process of sub-step(1.2). However, such fragments may vary significantly in size and intheir molecular weight, as the lignin-derived components vary.

Filtration may be selected from ultrafiltration and nanofiltration,which may be carried out by an ultrafiltration and/or nanofiltrationcell, preferably having a pre-filtration section for increasing theefficiency of the filtration step (e.g. avoidance of membrane blockade,e.g. by higher molecular weight lignin-derived components). Stirredultrafiltration cells as described by Duval et al. (Holzforschung 2015,69, 127-134) may be applied as well. Preferably, the ultrafiltrationand/or nanofiltration cell comprises at least one molecular weightcut-off unit, preferably at least two molecular weight cut-off unitsallowing to isolate lignin-derived precursor compounds within amolecular weight range, which reflects the molecular weight of monomericand dimeric target compounds, e.g. from 150 Da to 1.000 Da or from 150to 500 Da. Preferably, a cascade of cut-off units (e.g. strating withone or more ultrafiltration cell(s) and one or more subsequentnanofiltration cell(s) with preferably decreasing cut-off values may beemployed to fractionate the resulting lignin-derived decompositionproducts obtained in step (3). The decomposition products obtained instep (3) may usually be fractionated in solution or may be isolated asdried matter and be re-dissolved thereafter, if required.

Preferably, isolation sub-step (4.1) thus comprises filtration and/orextraction, preferably ultrafiltration and/or nanofiltration by anultrafiltration and/or nanofiltration cell, preferably having apre-filtration section. Filtration in sub-step (4.1) is preferablycarried out in a ultrafiltration and/or nanofiltration cell comprisingat least one molecular weight cut-off unit, preferably at least twomolecular weight cut-off units, wherein the at least one molecularweight cut-off unit has a cut-off level preferably of 1 kDa to 1.5 kDa.

Preferably, the ultra- and/or nanofiltration may be followed by furtherpurification steps (step 4.4) to increase purity of the lignin-derivedlmw (aromatic) precursor compounds. For example, diafiltration againstwater may be used to remove residual sugars and reactive agents from thelow molecular weight precursor compound fraction. Alternatively, thelignin-derived precursor compounds can be isolated by extraction,optionally followed by fractional distillation.

Decomposition reactions which are characterized by reaction conditionsbearing the risk of re-polymerization of the lignin-derived material tobe decomposed are preferably avoided by step (4) of the inventivemethod. Nevertheless, any such re-polymerized by-products may stillresult from step (4), which need to be eliminated downstream of theinventive method. Components other than the precursor compounds areeither discarded, e.g. for combustion, or recycled by another step ofdecomposition (e.g. a second decomposition reaction according to step(3)).

By step (4.1), monomeric or dimeric lignin-derived precursor compounds(obtained from the decomposition reaction of, e.g. lignosulfonate, bystep (3)) are isolated from the other fragments of the decompositionstep (3). Thereby, lignin-derived precursor compounds as described aboveare obtained. Said lignin-derived precursor compounds may be isolated inthe form of a (precursor) composition comprising or preferably(essentially) consisting of said precursor compounds, which(essentially) does not comprise higher molecular weight (aromatic)lignin components and/or preferably from other non-lignin-derivedresidual components, including e.g. inorganic reactive agents. It isparticularly envisaged that the lignin-derived (precursor) compositionobtained in step (4) comprises several species (i.e. a mixture) ofmonomeric and dimeric lignin-derived lmw (aromatic) precursor compoundsas defined above. Accordingly, the composition directly obtained fromsub-step (4.1) or from su-step (4.2) or (4.3) of the inventive methodmay comprise at least one lignin-derived lmw (aromatic) precursorcompound that comprises one or two aromatic (carbocyclic) ring(s),separated by a linker or directly linked by a bond (biphenyliccompound). A compound comprising two aromatic rings is typically derivedfrom two covalently linked monomers (dimer) of the modified ligninprecursor component as the intermediate of the inventive method.

The monomeric or dimeric precursor compounds isolated by sub-step (4.1)may be further modified according to the present invention. They maye.g. be oxidized or chemically modified by other reactions, which mayresult in modified substitution patterns or modified ring structures,e.g. result in annulated ring systems (such as naphthalene oranthracene-derived compounds). Thus, the lignin-derived precursorcompounds isolated by sub-step (4.1) may be subjected to other chemicalreactions (sub-steps (4.2, 4.3) and may thereby comprise functionalgroups or aromatic ring systems not occurring in the modifiedlignin-derived components obtained by step (2). They may, e.g., be ofhigher or lower oxidation state, they may contain functional groups notoccurring in natural lignin at all, and/or they may exhibit bi-, tri-,tetra- or pentacyclic (annulated) aromatic ring systems. A compoundcomprising two aromatic rings is typically derived from two covalentlylinked monomers (dimer) of the modified lignin-derived component as theintermediate of the inventive method. Specifically, the lignin-derivedprecursor compounds obtained from step (4) are intended for subsequentsulfonation according to step (5) to provide sulfonated redox activetarget compounds particularly envisaged for use as redox flow batteryelectrolytes.

Sub-Step (4.2): Annulation

A monocyclic precursor compound provided by any one of sub-steps (4.1),(4.3), (4.4) or (4.5) may either be provided as it is or preferably befurther reacted in a sub-step (4.2) to an annulated aromatic compound,comprising at least two annulated aromatic rings (also referred to as a“polycyclic” compound herein) and which may preferably be bi-, tri-,tetra- or pentacyclic. Annulated bicyclic or pentacyclic compounds maybe particularly preferred. They may be purified and further processedaccording to the present invention.

Such an aromatic annulated compound comprising more than one ring is ofparticular value as a precursor for further oxidation (sub-step (4.3)).

Said reaction type is typically known as annulation, which serves inorganic chemistry as a chemical reaction, which allows to anneal twoaromatic (mono-, di- or n-aromatic) ring systems.

Preferably, the two or more precursor molecules of the annulationreaction are both or all e.g. monomeric or dimeric target compounds. Theannulation is, for example, achieved by a Diels-Alder reaction or aFriedel-Crafts acylation.

It may be preferred that lignin-derived precursor compounds provided bysub-step (4.1) comprising one aromatic ring are further processed in asub-step (4.2), wherein said lignin-derived precursor compoundcomprising one aromatic ring is subjected to an annulation reaction,preferably a Diels-Alder reaction or a Friedel-Crafts acylation, whereinthe annulation reaction product may be a lignin-derived lmw aromatic bi-or tricyclic or polycyclic annulated precursor compound, wherein saidcompound may be characterized by general Formula (II), (III) or (IV)

-   1. The method according to claim 22, wherein the at least one    precursor compound comprises one aromatic ring and is further    processed in a sub-step (4.2), wherein said precursor compound    comprising one aromatic ring is subjected to an annulation reaction,    preferably a Diels-Alder reaction or a Friedel Crafts acylation,    wherein the annulation reaction product is a low molecular weight    aromatic bi- or tricyclic annulated aromatic compound, wherein said    compound is characterized by Formula (II), (III) or (IV)

-   -   wherein        -   each of R², R³, R⁵-R⁸ of Formula (II) is independently            selected from hydrogen, hydroxy, carboxy, linear or            branched, optionally substituted, C₁₋₆ alkyl, linear or            branched, optionally substituted, C₁₋₆ alkenyl, linear or            branched, optionally substituted, C₁₋₆ alcohol, linear or            branched, optionally substituted, C₁₋₆ aminoalkyl, linear or            branched, optionally substituted, C₁₋₆ carboxyalkyl, linear            or branched, optionally substituted, C₁₋₆ alkoxy, linear or            branched, optionally substituted, C₁₋₆ aldehyde, ester, oxo            or carbonyl, wherein preferably at least one of R², R³,            R⁵-R⁸ is hydroxy or C₁₋₃ alkoxy, and        -   R¹ and R⁴ of Formula (II) is/are selected from the group            consisting of hydrogen, hydroxy, linear or branched,            optionally substituted, C₁₋₆ carboxyl, linear or branched,            optionally substituted, C₁₋₆ aldehyde, and linear or            branched, optionally substituted, C₁₋₆ alcohol,        -   each of R¹-R¹⁰ of Formula (III) is independently selected            from hydrogen, hydroxy, carboxy, linear or branched,            optionally substituted, C₁₋₆ alkyl, linear or branched,            optionally substituted, C₁₋₆ alkenyl, linear or branched,            optionally substituted, C₁₋₆ alcohol, linear or branched,            optionally substituted, C₁₋₆ aminoalkyl, linear or branched,            optionally substituted, C₁₋₆ carboxyalkyl, linear or            branched, optionally substituted, C₁₋₆ alkoxy, linear or            branched, optionally substituted, C₁₋₆ aldehyde, ester, oxo            or carbonyl,        -   wherein preferably at least one of R², R⁵, R⁶ and R⁸ is            hydroxy or C₁₋₃ alkoxy, and        -   R¹, R⁴, R⁹ and R¹⁰ of Formula (III) is/are preferably            selected from the group consisting of hydrogen, hydroxy,            linear or branched, optionally substituted, C₁₋₆ carboxyl,            linear or branched, optionally substituted, C₁₋₆ aldehyde,            and linear or branched, optionally substituted, C₁₋₆            alcohol,        -   each of R², R³ and R⁷-R¹⁰ of Formula (IV) is independently            selected from hydrogen, hydroxy, carboxy, linear or            branched, optionally substituted, C₁₋₆ alkyl, linear or            branched, optionally substituted, C₁₋₆ alkenyl, linear or            branched, optionally substituted, C₁₋₆ alcohol, linear or            branched, optionally substituted, C₁₋₆ aminoalkyl, linear or            branched, optionally substituted, C₁₋₆ carboxyalkyl, linear            or branched, optionally substituted, C₁₋₆ alkoxy, linear or            branched, optionally substituted, C₁₋₆ aldehyde, ester, oxo            or carbonyl,        -   wherein preferably at least one of R², R³ and R⁷-R¹⁰ is            hydroxy or C₁₋₃ alkoxy, and        -   R¹, R⁴, R⁵ and R⁶ of Formula (IV) is selected from the group            consisting of hydrogen, hydroxy, linear or branched,            optionally substituted C₁₋₆ carboxyl, linear or branched,            optionally substituted, C₁₋₆ aldehyde, and linear or            branched, optionally substituted, C₁₋₆ alcohol.

Alternatively, said compound may be characterized by said compound maybe characterized by General Formula (II), (III) or (IV)

wherein

-   -   each of R²-R⁷ of Formula (II) is independently selected from H,        optionally substituted C₁₋₆ alkyl, optionally substituted C₁₋₆        alkenyl, halogen, optionally substituted C₁₋₆ alkoxy, amino,        nitro, phosphoryl, phosphonyl, wherein at least one of R², R⁴,        R⁵, and R⁷ is hydroxy or C₁₋₃ alkoxy, and    -   R¹ and/or R⁸ of Formula (II) is/are selected from the group        consisting of hydrogen, hydroxy, linear or branched C₁₋₆        carboxyl, linear or branched C₁₋₆ aldehyde, linear or branched        C₁₋₆ ketone, and linear or branched C₁₋₆ alcohol,    -   each of R²-R⁸ of Formula (III) is independently selected from H,        optionally substituted C₁₋₆ alkyl, optionally substituted C₁₋₆        alkenyl, halogen, optionally substituted C₁₋₆ alkoxy, amino,        nitro, phosphoryl, phosphonyl, wherein at least one of R², R⁴,        R⁵, R⁶ and R⁸ is hydroxy or C₁₋₃ alkoxy, and    -   R¹, R⁹ and/or R¹⁰ of Formula (III) is/are selected from the        group consisting of hydrogen, hydroxy, linear or branched C₁₋₆        carboxyl, linear or branched C₁₋₆ aldehyde, linear or branched        C₁₋₆ ketone, and linear or branched C₁₋₆ alcohol,    -   each of R²-R⁹ of Formula (IV) is independently selected from H,        optionally substituted C₁₋₆ alkyl, optionally substituted C₁₋₆        alkenyl, halogen, optionally substituted C₁₋₆ alkoxy, amino,        nitro, phosphoryl, phosphonyl, wherein at least one of R², R⁴,        R⁷, and R⁹ is hydroxy or C₁₋₃ alkoxy, and    -   R¹ and/or R¹⁰ of Formula (IV) is selected from the group        consisting of hydrogen, hydroxy, linear or branched C₁₋₆        carboxyl, linear or branched C₁₋₆ aldehyde, and linear or        branched C₁₋₆ alcohol.

(a) Friedel-Crafts Acylation

Preferably, the annulation reaction is a Friedel-Crafts acylation. Thisis particularly surprising as such acylation reactions were previouslyknown preferably in the petrochemical field with regard to annulationreactions. Transferring said annulation reaction to compounds accordingto the present invention from renewable sources opens new synthesisoptions.

Friedel-Crafts acylation is the acylation of aromatic rings with an acylchloride using a strong Lewis acid catalyst. Friedel-Crafts acylation isalso possible with acid anhydrides. This reaction typically involves theacylation of an aromatic ring with an alkyl halide using a strong Lewisacid catalyst, e.g. an anhydrous ferric chloride as a catalyst.

(b) Diels-Alder Reaction

In the context of the present invention, a Diels-Alder reaction isunderstood as an organic chemical reaction, typically a [4+2]cycloaddition, between a conjugated diene and a substituted alkene,commonly termed the dienophile, to form a substituted cyclohexenesystem. Said formed cyclohexene system is preferably aromatic. TheDiels-Alder reaction is particularly useful in synthetic organicchemistry as a reliable method for forming 6-membered systems with goodcontrol over regio- and stereochemical properties.

For example, through the conduction of a Diels-alder reaction, amonocyclic compound provided by sub-step (4.1) of the present inventionmay be extended to a bicyclic, tricyclic, tetracyclic or even highern-cyclic compound. Without wanting to be bound by theory, it is believedthat compounds with increased annulation are advantageous as furtherprocessed redox active compounds. For example, anthracene derivatives,which may be precursors for anthraquinone-derivatives, are one preferredexample in the context of the present invention as they show that redoxpotentials decrease with increased annulation and, thus, the moreannulated derivatives are more stable. This is of particular importancefor compounds, which—according to a further aspect of the presentinvention—are preferably oxidized and sulfonated to a redox activetarget compound for versatile use, which compound advantageouslyrequires a long operational life to be fit for practice. By providingredox active target compounds of increased stability, this importantpractical demand is met.

With an appropriate selection of a diene, it is possible to convertbenzoquinone structures to naphthacenes, anthracene and/orphenanthrenes. The fusion of a benzene ring onto an existing monocycliccompound according to the present invention, preferably an oxidizedcompound such as quinone, may be accomplished on a ring which has twoadjacent positions unsubstituted or substituted. However, unsubstitutedpositions are generally preferred due to higher yields. Hence, it ispreferred in the context of the present invention that if a compound ofmore than one aromatic ring is desired, compounds are preferablysubjected to further substitution reactions only after the annulationreaction was performed. It may be further advantageous in large-scalereactions to add one or more polymerization inhibitors known in the art.The Diels-alder reaction may be catalysed by any suitable catalyst knownin the art, preferably by one or more metallic chlorides and/orzeolites. The subsequent oxidation step may or may not be necessary. Ifa reduced catalyst is still present from earlier reaction steps, thenewly annulated ring may be instantly oxidized and aromatized, yieldingin a multi-ring quinone. Alternatively, aeration in alkaline solutionmay be used, e.g., to obtain an anthraquinone derivative.

The condensation is preferably carried out prior to the optionaldownstream oxidation, and/or prior to derivatization in order to avoid,e.g. steric hindrance, and, in consequence, lower yields in condensedand derivatized product.

Sub-Step (4.3) Oxidation of Precursor Compounds

Preferably, monocyclic or annulated precursor compounds obtained fromany one of sub-steps (4.1), (4.2), (4.4) or (4.5), respectively, aremodified in a sub-step (4.3) by oxidation in the presence of (i) anoxidizing agent selected from the group consisting of H₂O₂, O₂ and air,and (ii) a heterogeneous catalyst comprising a metal ion or a metalloid,or performing homogeneous catalysis in the presence of NaOH (in whichcase, usually no catalyst comprising a metal ion or a metalloid isrequired). Preferably, said oxidation reaction yields at least onequinone and/or hydroquinone compound, or a composition comprising thesame.

Preferably, Co(II) complexes may be employed because they have a highselectivity towards quinones. For example, (pyr)Co(II)salen may beemployed in the presence of O₂ at overpressure, e.g. at least 3 bar.Such a reaction may preferably be conducted at room temperature in anorganic solvent such as MeOH. Other preferred catalysts areCo(3-methoxysalen) and Co(N—N-Me salpr). In the latter case, thepreferred organic solvent may be CH₂Cl₂. Said oxidation provides anoxidized lignin-derived lmw aromatic precursor compound, which isgenerally understood herein as hydroquinone compound according to thepresent invention and/or, upon further oxidation, as a quinone compoundaccording to the present invention.

(a) Oxidation of Monocyclic Precursor Compounds to Hydroquinones

Oxidation of monocyclic precursor compounds preferably yields at leastone hydroquinone compound (step (4.3)(a)), characterized by generalFormula (Va):

-   -   wherein each of R¹-R⁵ is independently selected from hydrogen,        hydroxy, carboxy, linear or branched, optionally substituted,        C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆        alkenyl, linear or branched, optionally substituted, C₁₋₆        alcohol, linear or branched, optionally substituted, C₁₋₆        aminoalkyl, linear or branched, optionally substituted, C₁₋₆        carboxyalkyl, linear or branched, optionally substituted, C₁₋₆        alkoxy, linear or branched, optionally substituted, C₁₋₆        aldehyde, ester, oxo or carbonyl, and wherein one of R¹, R³ and        R⁵ is hydroxy;

or by general formula (Vb),

-   -   wherein each of R¹-R⁹ is independently selected from hydrogen,        hydroxy, carboxy, linear or branched, optionally substituted,        C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆        alkenyl, linear or branched, optionally substituted, C₁₋₆        alcohol, linear or branched, optionally substituted, C₁₋₆        aminoalkyl, linear or branched, optionally substituted, C₁₋₆        carboxyalkyl, linear or branched, optionally substituted, C₁₋₆        alkoxy, linear or branched, optionally substituted, C₁₋₆        aldehyde, ester, oxo or carbonyl; and wherein R⁵ is preferably        hydroxy.    -   Alternatively, oxidation of monocyclic precursor compounds may        yield at least one hydroquinone compound (step (4.3)(a)),        characterized by general Formula (Va):

-   -   wherein each of R¹-R⁵ is independently selected from optionally        substituted C₁₋₆ alkyl, optionally substituted C₁₋₆ alkenyl,        halogen, optionally substituted C₁₋₆ alkoxy, amino, carboxyl,        nitro, phosphoryl, and phosphonyl, and wherein one of R¹, R³ and        R⁵ is hydroxy;        or by general formula (Vb),

-   -   wherein each of R¹-R⁹ is independently selected from optionally        substituted C₁₋₆ alkyl, optionally substituted C₁₋₆ alkenyl,        halogen, optionally substituted C₁₋₆ alkoxy, amino, carboxyl,        nitro, phosphoryl, and phosphonyl; and wherein R⁵ is hydroxy.

Said hydroquinone compound is preferably a redox active compound, whichmay be beneficial in a variety of uses. Specifically, said hydroquinonecompound may be further oxidized (e.g. in step (3)(b)) and/or subjectedto a sulfonation reaction according to step (5) of the inventive method,wherein the resulting sulfonated redox active (hydro-)quinone compoundis intended for use as a redox flow battery electrolyte.

(b) Oxidation of Monocyclic Precursor Compounds to Quinones

It is particularly preferred that step (4.3)—under harsher oxidationconditions than in step (4.3(a))—provides at least one quinone compound(step 4.3(b)), characterized by any of general Formulae (VIa) to (VIb):

-   -   wherein each of R¹-R² and R⁴-R⁵ is independently selected from        hydrogen, hydroxy, carboxy, linear or branched, optionally        substituted, C₁₋₆ alkyl, linear or branched, optionally        substituted, C₁₋₆ alkenyl, linear or branched, optionally        substituted, C₁₋₆ alcohol, linear or branched, optionally        substituted, C₁₋₆ aminoalkyl, linear or branched, optionally        substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally        substituted, C₁₋₆ alkoxy, linear or branched, optionally        substituted, C₁₋₆ aldehyde, ester, oxo or carbonyl; or

-   -   wherein each of R²-R⁵ is independently selected from hydrogen,        hydroxy, carboxy, linear or branched, optionally substituted,        C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆        alkenyl, linear or branched, optionally substituted, C₁₋₆        alcohol, linear or branched, optionally substituted, C₁₋₆        aminoalkyl, linear or branched, optionally substituted, C₁₋₆        carboxyalkyl, linear or branched, optionally substituted, C₁₋₆        alkoxy, linear or branched, optionally substituted, C₁₋₆        aldehyde, ester, oxo or carbonyl; or

-   -   wherein each of R¹-R⁴ is independently selected from hydrogen,        hydroxy, carboxy, linear or branched, optionally substituted,        C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆        alkenyl, linear or branched, optionally substituted, C₁₋₆        alcohol, linear or branched, optionally substituted, C₁₋₆        aminoalkyl, linear or branched, optionally substituted, C₁₋₆        carboxyalkyl, linear or branched, optionally substituted, C₁₋₆        alkoxy, linear or branched, optionally substituted, C₁₋₆        aldehyde, ester, oxo or carbonyl; or

-   -   wherein each of R¹-R⁴ and R⁶-R⁹ is independently selected from H        hydrogen, hydroxy, carboxy, linear or branched, optionally        substituted, C₁₋₆ alkyl, linear or branched, optionally        substituted, C₁₋₆ alkenyl, linear or branched, optionally        substituted, C₁₋₆ alcohol, linear or branched, optionally        substituted, C₁₋₆ aminoalkyl, linear or branched, optionally        substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally        substituted, C₁₋₆ alkoxy, linear or branched, optionally        substituted, C₁₋₆ aldehyde, ester, oxo or carbonyl.    -   Alternatively, step (4.3)—under harsher oxidation conditions        than in step (4.3(a))—provides at least one quinone compound        (step 4.3(b)), may yield a compound characterized by any of        general Formulae (VIa) to (VIb):

-   -   wherein each of R¹-R² and R⁴-R⁵ is independently selected from        optionally substituted C₁₋₆ alkyl, optionally substituted C₁₋₆        alkenyl, halogen, optionally substituted C₁₋₆ alkoxy, amino,        carboxyl, nitro, phosphoryl, and phosphonyl; or

-   -   wherein each of R²-R⁵ is independently selected from optionally        substituted C₁₋₆ alkyl, optionally substituted C₁₋₆ alkenyl,        halogen, optionally substituted C₁₋₆ alkoxy, amino, carboxyl,        nitro, phosphoryl, and phosphonyl; or

-   -   wherein each of R¹-R⁴ is independently selected from optionally        substituted C₁₋₆ alkyl, optionally substituted C₁₋₆ alkenyl,        halogen, optionally substituted C₁₋₆ alkoxy, amino, carboxyl,        nitro, phosphoryl, and phosphonyl; or

-   -   wherein each of R¹-R⁴ and R⁶-R⁹ is independently selected from        H, optionally substituted C₁₋₆ alkyl, halogen, optionally        substituted C₁₋₆ alkoxy, amino, nitro, carboxyl, phosphoryl, and        phosphonyl.

Quinone compounds characterized by any of Formulas (VI a) to (VI d) mayalso be provided by oxidizing the at least one hydroquinone compoundprovided by step (4.3(a)), for instance, in the cell stack of a batteryor by an oxidant, optionally in the presence of a heterogeneouscatalyst. Usually, it is sufficient to provide a hydroquinone compound,which compound is redox active and may be oxidized or a part of thetotal amount of employed molecules of said hydroquinone compound maybecome oxidized.

It may be preferred to simultaneously accomplish both chemicaldecomposition of modified lignin-derived components (step (3)) andoxidation of lignin-derived precursor (optionally hydroquinone)compounds (sub-step 4.3 (a)-(c)). Therein, for example, (cracking and)oxidizing of a modified lignin-derived component (typically alternative(3(a)) or (3(c)) takes place, and instantaneously or concurrently, thecomponent is oxidized to a (hydro-)quinone compound according to thepresent invention. Further, the step may involve an addition reaction tointroduce further substituents of interest under suitable reactionconditions.

Advantageously, said combination may save time and resources in terms ofreactants, reactive agents and/or process equipment and apparatus means.Accordingly, such a combination leads to significant more economic andsimple method for producing redox active precursor compounds ofrenewable origin such as the (hydro-)quinone compounds according to thepresent invention. Such a combined method step is preferably facilitatedby applying electrooxidation of step (3(c)), but catalyst-facilitatedoxidation under (3(a)) may also be applied. Electrooxidation ispreferred, wherein direct oxidation from a modified lignin such aslignosulfonate to a (hydro-)quinone compound is controlled by therespective set electrochemical conditions. Preferably, the modifiedlignin is diluted to a concentration below 20% (w/w), preferably below10% (w/w), more preferably below 5% (w/w), even more preferably below 2%(w/w). The solution may have a pH of 1 to 14. Electrooxidation underacidic conditions is preferred. Alternatively, under alkalineconditions, the preferred pH is at least 11, more preferably at least13. Electrooxidation is preferably conducted in a flow cell, wherein theflow is at least corresponding to 1 ml/min, preferably 10 ml/min or 50ml/min, more preferably at least 200 ml/min, but may be up-scaled tosignificantly higher flows. Electrolysis may typically be conductedgalvanostatically, preferably for at least 10 min, preferably at leastmin, alternatively for at least 1 hour, preferably for at least 4 hours.Most preferred is a time period for conducting electrolysis of at least30 min, e.g. to save time and resources. Preferably, electrolysis iscarried out by applying a current of preferably at least 0.5 mA/cm²,more preferably 1 mA/cm², even more preferably at least 5, 10 or 100mA/cm².

Oxidation of the hydroquinone compound obtained in sub-step (4.3(a)) mayfor example provide a compound represented by one or both of thefollowing structures:

-   Wherein in the compound according to Formula (VIa-f), R¹, R³, R⁵ are    independently selected from H, OH oder C₁-C₆ methoxy, preferably    methoxy.

(c) Oxidation of Annulated Polycyclic Precursor Compounds to(Hydro-)Quinones,

It is also preferred that (annulated) polycyclic precursor compoundsobtained from sub-step (4.2) (in particular lignin-derived low molecularweight bi- or tricyclic aromatic precursor compounds) are furthermodified in a sub-step (4.3(c)) by oxidizing said precursor compound inthe presence of (i) an oxidizing agent selected from the groupconsisting of H₂O₂, O₂ and air, and (ii) a heterogeneous catalystcomprising a metal ion or a metalloid, or performing homogeneouscatalysis in the presence of NaOH (in which case, usually no catalystcomprising a metal ion or a metalloid is required), to obtain at leastone quinone and/or hydroquinone compound, wherein said compound ischaracterized by any of general Formula (VII), (VIII) and/or (IX):

-   -   wherein each of R¹-R⁸ with regard to Formula (VII) and/or each        of R¹-R¹⁰ with regard to Formula (VIII) and (IX) is        independently selected from hydrogen, hydroxy, carboxy, linear        or branched, optionally substituted, C₁₋₆ alkyl, linear or        branched, optionally substituted, C₁₋₆ alkenyl, linear or        branched, optionally substituted, C₁₋₆ alcohol, linear or        branched, optionally substituted, C₁₋₆ aminoalkyl, linear or        branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or        branched, optionally substituted, C₁₋₆ alkoxy, linear or        branched, optionally substituted, C₁₋₆ aldehyde, ester, oxo or        carbonyl;    -   wherein at least one of R⁸ and R⁵ or R¹ and R⁴ of Formula (VII)        are hydroxy or oxo, or at least one of R⁹ and R⁶, R¹⁰ and R⁵, or        R¹ and R⁴ of Formula (VIII) are hydroxy or oxo, or at least one        of R¹⁰ and R⁷ or R¹ and R⁴ of Formula (IX) are hydroxy or oxo.    -   Alternatively, said compound may be characterized by any of        general Formula (VII), (VIII) and/or (IX):

-   -   wherein each of R¹-R⁸ with regard to Formula (VII) and/or each        of R₁-R¹⁰ with regard to Formula (VII) and (IX) is independently        selected from H, optionally substituted C₁₋₆ alkyl, halogen,        optionally substituted C₁₋₆alkoxy, amino, nitro, carboxyl,        phosphoryl, phosphonyl;    -   wherein at least one of R⁸ and R⁵ or R¹ and R⁴ of Formula (VII)        are hydroxy or oxo, or at least one of R⁹ and R⁶, R¹⁰ and R⁵, or        R¹ and R⁴ of Formula (VIII) are hydroxy or oxo, or at least one        of R¹⁰ and R⁷ or R¹ and R⁴ of Formula (IX) are hydroxy or oxo.

For example, sub-step (4.3(c)) may provide a compound characterized bythe following structure:

Sub-Step (4.4): Purification

It is further preferred that the at least one lignin-derived precursorcompound (preferably a quinone and/or hydroquinone compound), providedby sub-step (4.3)(a)-(c) may preferably be subjected to a purificationsub-step (4.4) to separate said compound (or the composition comprisingthe same) from residual (for example non-(hydro-)quinone) compounds by asuitable method, preferably by preferably precipitation,recrystallization, distillation, sublimation, solid phase extraction orfluid-fluid phase extraction as generally known in the art.

Said at least one purified (hydro-)quinone is typically a redox activecompound. The at least one purified (hydro-)quinone is subsequentlysubjected to sulfonation step (5) of the inventive method in order toobtain sulfonated (and optionally further derivatized) redox activecompounds (or compositions comprising or (essentially) consisting of thesame) that exhibit superior redox characteristics and are thereforeparticularly useful as redox flow battery electrolytes.

Sub-Step (4.5) Derivatization

Lignin-derived precursor compounds provided by step (4) may preferablybe subjected to a further derivatization step. Therein, lignin-derivedprecursor compounds preferably according to any one of structuralformulae (I) to (IX) are modified to introduce at least one or moregroups selected from hydrogen, hydroxy, carboxy, linear or branched,optionally substituted, C₁₋₆ alkyl (e.g. —CH₃), linear or branched,optionally substituted, C₁₋₆ alkenyl, linear or branched, optionallysubstituted, C₁₋₆ alcohol, linear or branched, optionally substituted,C₁₋₆ aminoalkyl, linear or branched, optionally substituted, C₁₋₆carboxyalkyl, alkoxy, in particular linear or branched, optionallysubstituted, C₁₋₆ alkoxy, linear or branched, optionally substituted,C₁₋₆ aldehyde, ester, halogen, amine (e.g. —NH₂), amino, amide, nitro,oxo, carbonyl, phosphoryl, phosphonyl or cyanide groups, into theprecursor compounds at a position of the aryl structure other than thosecharacterized by an oxo or hydroxyl group, wherein said group(s) is/aredirectly bound to the aryl structure or bound via an alkyl linker to thearyl structure, preferably via a methyl linker. Any other suitableorganic group may also be introduced. Advantageously, said groups mayconfer beneficial properties in terms of redox behaviour or solubilityof the resulting compound. Nitro groups (NO₂ ⁻) may be introduced butmay be less preferred for stability reasons of the resulting compound.

The derivatization reactions can be performed with benzoquinones,benzohydroquinones and their derivatives, naphthoquinones,naphthohydroquinones and their derivatives and anthraquinones,anthrahydroquinones and their derivatives as starting materials as wellas mixtures of the starting materials. Each starting material,intermediate or product can be transferred to its corresponding quinoneor hydroquinone form via oxidation or reduction. Suitable oxidizationagents may be selected from be air, oxygen or hydrogen peroxide, incombination with or without catalysts. The catalysts may be selectedfrom metal based-catalysts (preferably comprising copper and aluminium),iodine, non-organic and organic acids or other quinones. Suitablereduction agents may be hydrogen, sodium dithionate, sodium borohydride,iron, tin(II)-chloride or zinc, in combination with or withoutcatalysts, with hydrogen and sodium dithionate being preferred. Thecatalysts may be metal based, preferably palladium or nickel.

Quinones and hydroquinones can be modified or derivatized bysubstitution and addition reactions or rearrangements, preferablysubstitution reactions on hydroquinones and addition reactions onquinones (cf. reaction schemes 1 and 2). Substitution reactions includeany reaction wherein a proton on the aromatic ring is exchanged by adifferent group, e.g. via an electrophile substitution. Suitableelectrophiles may be selected from sulfur trioxide, aldehydes, ketones,esters, lactone, carboxylic acids, anhydrides, imine, carbon dioxide,chlorosulfonic acid, acyl halides, halogens, NO₂ and epoxides,preferably carbon dioxide, anhydrides, imines and acyl halides.

Addition reactions include any reaction that introduces a new group inthe aromatic ring except for protons, preferably via a nucleophileaddition on the aromatic ring with subsequent tautomeric rearrangement.Suitable nucleophiles include ammonia, amines, nitrogen containingheterocycles, thiols, alcohols, cyanides and azides, preferably amines,alcohols and nitrogen containing heterocycles.

Reactions can be performed step wise or in several steps in a one potreaction. The modified target compounds may exhibit favorable redoxproperties rendering them useful in a variety of applications.

Further substituents can be introduced into napthoquinones andnapthohydroquinones after the modification reaction on R²-R⁵ (Scheme 2).Typical (further) substituents R²-R⁵ are hydrogen, methoxy, ethoxy,primary, secondary, tertiary and quaternary amines, carboxyalkyl,aminoalkyl, carboxylic acids, esters, amides, cyanides and alkyl-groups.

Anthaquinones and anthrahydroquinones can be modified by oxidation andreduction as described in the context of other (hydro-)quinones above.Subsequently, substituents can be introduced on R²-R¹⁰ in suitablesubstitution reactions, which typically do not involve electrophilicsubstitution.

Sulfonation of (hydro-)quinones (in particular benzo-, naphtho- andanthraquinones) is a modification reaction of particular interest in thecontext of the present invention.

Step (5): Sulfonation

Subsequently, the lignin-derived (optionally derivatized) precursorcompounds (or the composition comprising or (essentially) consisting ofsaid precursor compounds) obtained from any one of the sub-steps(4.1)-(4.5) of previous step (4), are further subjected to a sulfonationstep (5) to yield the target compounds (or the composition comprisingthe same) according to the present invention. Sulfonation is envisagedto improve solubility and/or electrochemical properties and/or stabilityof the resulting target compounds.

By applying the sulfonation step (5), at least one sulfonyl (SO₃H)group(s) is/are introduced into the lignin-derived precursor compounds,preferably according to any one of structural formulae (I) to (IX) at aposition of the aryl structure other than those characterized by an oxoor hydroxyl group, wherein said group(s) is/are directly bound to thearyl structure. The resulting target compounds—i.e. sulfonatedlignin-derived lmw aromatic target compounds as defined herein—areuseful as redox active species in redox flow batteries. Notably, thetarget compounds may optionally be subjected to a further derivatizationstep subsequent to sulfonation.

In order to obtain the lignin-derived composition according to thepresent invention (and/or the sulfonated lignin-derived target compoundscomprised by the same), lignin-derived precursor compounds (orcompositions comprising or (essentially consisting of the same) aresubjected to a sulfonation reaction. In general, sulfonation may becarried out in the presence of concentrated aqueous sulfuric acid.Alternatively, sulfur trioxide may be mixed with inert gas, such as air,N₂ and/or CO₂, or complexed with a complexing agent such as pyridine,dioxane, (CH₃)₃N or DMF. Typically, sulfonation is preferably performedat higher temperatures due to increased resulting yields. Therein, anincreased temperature is understood to be at least 50° C., preferably100° C. However, the temperature shall preferably not decompose themodified compound by pyrolysis. Accordingly, the temperature shouldpreferably be lower than 200° C. Separation of the resulting sulfonatedcompound(s) may subsequently be carried out, for example, by filtrationor salting out as described herein.

Sulfonation of (hydro-)quinones, e.g. benzo- and naphtha(hydro)quinones,may be accomplished as shown in Scheme 1 and 2 for the derivatizationsub-step (4.5) above. The terms “sulfonation” and “sulfonation reaction”are used herein to refer to a derivatization reaction whereby at leastone sulfonyl group is introduced into a compound.

The sulfonation step according to the inventive method typicallyincludes as sub-step (i) the treatment of the lignin-derived precursorcompounds (or composition comprising the same), preferably a(hydro-)quinone compound (including benzo-, naphtha- and anthraquinones)with SO₃, either from oleum or SO₃ gas, as depicted in FIG. 1 and FIG. 2. The reaction is preferably performed under atmospheric pressure orelevated pressure in concentrated sulfuric acid at a temperature of40-300° C., preferably 60-120° C. for benzohydroquinones and 160-180° C.for anthraquinones. The reaction is undergone within 1-6 hours,preferably 3 hours for benzoquinones and 4 hours for anthraquinones.

After the reaction, the concentrated sulfuric acid may preferably bepoured into water and partiall neutralized (sub-step (ii)). Thepreferred neutralizing agent is calcium hydroxide, the terminativesulfuric acid concentration is 5-30%, preferably 10-20%. After partiallyneutralizing the sulfuric acid, the precipitated sulfate may be filteredoff (sub-step (iiia)). Subsequently, the resulting mixture may bedirectly concentrated (sub-step (iva)), preferably under reducedpressure to yield a solution of 0.4-1.5 mol/L active material and 10-40%sulfuric acid (FIG. 1 ). Alternatively, the solution is completelyneutralized (sub-step (iiib)) either with the same or anotherneutralizing agent and the water is then evaporated under reducedpressure (sub-step (ivb) (FIG. 2 ). Additional sulfates that eventuallyprecipitate are filtered off (sub-step (vb)) such that the productprecipitates. The remaining water is then evaporated (sub-step (vib) andthe solid is dried to yield a mixture of 30-90% sulfonated product mixedwith sulfates. Either process typically yields a crude mixture ofdifferently sulfonated lignin-derived lmw aromatic target compounds(such as sulfonated hydroquinones, naphthaquinones or anthraquinones).

Notably, the present inventors discovered that this solution may beapplied for instant use or upon concentration for the application as anelectrolyte in redox flow batteries. Thus, step (5) (and optionally step(6)) yields a lignin-derived composition comprising at least onesulfonated lignin-derived lmw (aromatic) target compound that is usefulas an electrolyte in a redox flow battery.

Preferred sulfonated (optionally lignin-derived) lmw (aromatic) targetcompound are specified in the section “Redox active compounds andcompositions” and in Tables 1-3 above. Preferred compositions maycomprise or (essentially) consist of 1,4-benzoquinone-2,5-disulfonicacid, 1,4-benzoquinone-2,6-disulfonic acid, 1,4-benzoquinone-2-sulfonicacid, 1,4-naphthoquinone-2,6-disulfonic acid,1,4-naphthoquinone-2,7-disulfonic acid,1,4-naphthoquinone-5,7-disulfonic acid, 1,4-naphthoquinone-5-sulfonicacid, 1,4-naphthoquinone-2-sulfonic acid,9,10-anthraquinone-2,6-disulfonic acid,9,10-anthraquinone-2,7-disulfonic acid,9,10-anthraquinone-1,5-disulfonic acid, 9,10-anthraquinone-1-sulfonicacid, 9,10-anthraquinone-2-sulfonic acid, or derivatives or a mixturethereof.

Step (6): Further Derivatization

Sulfonated lignin-derived target compounds provided by step (5) may besubjected to a further derivatization step. Therein, sulfonatedlignin-derived target compounds preferably according to any one ofstructural formulae (X) to (XV) are modified to introduce at least oneor more groups selected from hydrogen, hydroxy, carboxy, linear orbranched, optionally substituted, C₁₋₆ alkyl, linear or branched,optionally substituted, C₁₋₆ alkenyl, linear or branched, optionallysubstituted, C₁₋₆ alcohol, linear or branched, optionally substituted,C₁₋₆ aminoalkyl, linear or branched, optionally substituted, C₁₋₆carboxyalkyl, linear or branched, optionally substituted, C₁₋₆ alkoxy,linear or branched, optionally substituted, C₁₋₆ aldehyde, ester,halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl,phosphonyl, cyanide and sulfonyl groups, into the sulfonated targetcompounds at a position of the aryl structure other than thosecharacterized by an oxo or hydroxyl or sulfonyl group. Said group(s)is/are directly bound to the aryl structure or bound via an alkyl linkerto the aryl structure, preferably via a methyl linker. (Optional)derivatization according to step (6) of the inventive method maypreferably accomplished as described in the context of (optional)sub-step (4.5) above. Either one of sub-steps (4.5) and step (6), orboth, may be applied.

Sulfonated (and optionally further derivatized) redox active targetcompounds provided by step (5) (and as discussed above) of the inventivemethod may be used as electrolytes. Sulfonated oxidized annulatedcompounds preferably are superb redox active compounds for versatileuse. It is especially preferred that they may be produced from renewablesources. The inventive method allows to valorize otherwise wasteby-products from the pulping industry.

Step (7): Purification

The inventive method may optionally comprise a further purification step(7). Thereby, the sulfonated (and optionally further derivatized)lignin-derived target compound obtained from step (5) or step (6) of theinventive method (or the composition comprising the same) is separatedfrom residual for example non-(hydro-)quinone and/or non-sulfonated anddecomposed material. Purification may preferably be accomplished byemploying an extraction method, preferably precipitation,recrystallization, distillation, sublimation, solid phase extraction orfluid-fluid phase extraction as generally known in the art.

Step (8) Providing Redox Flow Battery Electrolytes

Preferably, the inventive method may comprise, optionally after step(5), (6) or (7) described herein, a step (8) of providing the obtainedredox active compounds or compositions comprising the same as redox flowbattery electrolytes. Step (8) is described herein as part of theinventive method of valorizing lignin by producing sulfonated targetcompounds therefrom, but is equally applicable to methods that employcrude oil, coal or pure organic substances as a starting material.

Specific structural characteristics of the compounds used (optionally inthe form of compositions) as redox flow battery electrolytes accordingto the invention are described in the section “Redox active compoundsand compositions” above. The term “(redox flow battery) electrolyte” asused herein refers to a substance that is capable of conductingelectrical currents via electron transfer in a redox flow battery.Electrolytes that are dissolved in a suitable medium for use in redoxflow batteries (e.g. water) are referred to as “electrolyte solutions”herein.

Sulfonated (optionally lignin-derived) target compounds (i.e. preferablysulfonated (hydro-)quinones as described below) and compositionscomprising or (essentially) consisting thereof are preferred redox flowbattery electrolytes according to the present invention.

When employed as redox flow battery electrolytes, sulfonated (optionallylignin-derived) target compounds (i.e., preferably sulfonated(hydro-)quinones as described herein) are typically comprised by anelectrolyte solution. Said “electrolyte solution” thus comprises atleast one electrolyte and a solvent. The electrolyte is preferably atleast one sulfonated (optionally lignin-derived) target compound(preferably a sulfonated (hydro-)quinone as described herein) orcomposition, which is dissolved or suspended in a suitable solvent. Thesolvent is typically selected from water, methanol, ethanol,dimethylsulfoxide, acetonitrile, acetone and glycol. The electrolytesolution may comprise further additives, including acids, bases,buffers, ionic liquids, stabilizers, and the like.

Sulfonated (optionally lignin-derived) target compounds or compositionsas disclosed herein may be used as catholytes and/or anolytes. The term“catholytes” refers to the part or portion of an electrolyte, which ison the cathode side of a redox-flow battery half-cell, whereas the term“anolyte” refers to the part or portion of an electrolyte, which is onthe anode side of a redox-flow battery half-cell. It is conceivable toemploy the inventive (optionally lignin-derived) target compounds bothas catholytes and anolytes in each half-cell (i.e. anode side andcathode side) of the same redox flow battery, thereby providing an“all-organic” redox flow battery. It is however also conceivable toprovide the sulfonated (optionally lignin-derived) target compounds orcompositions according to the invention as either catholytes or anolytesin a “half-organic” redox flow battery. Therein, sulfonated (optionallylignin-derived) target compounds or compositions are utilized either asanolytes (catholytes), whereas the catholyte (anolyte) comprises aninorganic redox active species. Examples for such inorganic redox activespecies include transition metal ions and halogen ions, such asVCl₃/VCl₂, Br⁻/ClBr₂, Cl₂/Cl⁻, Fe²⁺/Fe³⁺, Cr³⁺/Cr²⁺, Ti³⁺/Ti²⁺, V³⁺/V²⁺,Zn/Zn²⁺, Br₂/Br⁻, I³⁻/I⁻, VBr₃/VBr₂, Ce³⁺/Ce⁴⁺, Mn²⁺/Mn³⁺, Ti³⁺/Ti⁴⁺,Cu/Cu⁺, Cu⁺/Cu²⁺, and others.

Generally, a catholyte is charged when a redox couple is oxidized to ahigher one of two oxidation states, and is discharged when reduced to alower one of the two oxidation state:

Cathode (Positive Electrode):

(C: Catholyte)

${C^{n\overset{yields}{\rightarrow}}C^{n - z}} + {{ze}^{-}({Charge})}$${C^{n - z} + {ze}^{-}}\overset{yields}{\rightarrow}{C^{n}({Discharge})}$

In contrast, an anolyte is charged when a redox couple is reduced to alower one of two oxidation states, and is discharged when oxidized to ahigher one of the two oxidation states:

Anode (Negative Electrode):

${A^{n - x} + {xe}^{-}}\overset{yields}{\rightarrow}{A^{n}({Charge})}$${A^{n\overset{yields}{\rightarrow}}A^{n - x}} + {{xe}^{-}({Discharge})}$

(A: Anolyte)

The standard (redox flow battery) cell potential (E^(o) _(cell)) is thedifference in the standard electrode potentials (against the standardhydrogen electrode (SHE)) of the two half-cell reactions of thecatholyte and anolyte.

E ⁰ _(cell) =E ⁰ _(cat) −E ⁰ _(an)  eq.1

(E^(o) _(cell)=(redox flow battery) cell potential under standardconditions, E^(o) _(cat): standard reduction potential for the reductionhalf reaction occurring at the cathode, E^(o) _(an): standard reductionpotential for the oxidation half reaction occurring at the anode).

The Nernst Equation (eq. 2) enables the determination of cell potentialunder non-standard conditions. It relates the measured cell potential tothe reaction quotient and allows the accurate determination ofequilibrium constants (including solubility constants).

$\begin{matrix}{E_{cell} = {E_{cell}^{0} - {\frac{RT}{nF}\ln Q}}} & {{eq}.2}\end{matrix}$

(E_(cell)=(redox flow battery) cell potential under non-standardconditions, n=number of electrons transferred in the reaction, F=Faradayconstant (96,500 C/mol), T=Temperature and Q=reaction quotient of theredox reaction).

The redox flow battery cell potential thus depends on the concentrationand types of reactants (which determines the number of transferredelectrons and the reaction quotient). It will be understood that a redoxflow battery employing the sulfonated (optionally lignin-derived) targetcompounds or compositions according to the invention as a catholyteand/or anolyte preferably exhibit high (standard) cell potentials.Preferably, the redox flow battery employing (a) sulfonatedlignin-derived target compound(s) as catholyte and/or anolyte exhibits acell potential of at least +0.5 V, preferably at least +0.8 V, morepreferably at least +1.0 V, or more, typically between +0.5 and +1.5 V,preferably between +0.8 and +1.2 V for the open circuit voltage (OCV) inthe fully charged state. Suitable stabilizers can enhance the cellpotential to a range typically between +0.5 V and +2.5 V against SHE.

Sulfonated (optionally lignin-derived) target compounds intended for useas catholytes (accepting electrons in a reduction reaction) thuspreferably exhibit standard reduction potentials (against SHE) E^(o)_(cat) that are more positive (less negative) than the standardreduction potential for the employed anolyte (E^(o) _(an)). Preferably,sulfonated (optionally lignin-derived) target compounds intended for useas catholytes exhibit positive standard reduction potentials E⁰ _(cat)of more than 0 V, more preferably of at least +0.5 V, most preferably atleast +0.7 V against SHE.

Sulfonated (optionally lignin-derived) target compounds intended for useas anolytes (donating electrons in an oxidation reaction) thuspreferably exhibit standard reduction potentials (against SHE) E⁰ _(an)that are more negative (less positive) than the standard reductionpotential for the employed catholyte (E⁰ _(cat)). Preferably, sulfonatedlignin-derived target compounds intended for use as anolytes exhibitnegative standard reduction potentials of less than +0.3 V, preferably+0.1 V or less against SHE.

The standard reduction potential of the redox couple is characteristicof the molecule and its specific substituent groups and is inter aliarelated to the electronic energy of the molecular orbitals. The additionof sulfonic acid groups preferably increases the standard reductionpotential, which is consistent with the lowering of molecular orbitalenergies by electro-withdrawing groups.

While the equilibrium potentials of electrolytes in the cathodic andanodic half-cells determines the cell voltage, its capacity depends onthe effective electrolyte concentration, which is the solubilitymultiplied by the number of electrons transferred in the redoxreactions. Highly soluble electrolytes therefore preferably increase theenergy capacity of the redox flow battery and are therefore preferred.

Advantageously, (additional) sulfonyl groups are capable of increasingthe solubility of the sulfonated compound(s) in water, which preferablyprovides for an electrolyte solution usable in redox flow batteriesexhibiting a high capacity. The sulfonated (optionally lignin-derived)target compounds according to the invention are preferably soluble inconcentrations of at least 0.3 M, preferably at least 0.6 M, morepreferably at least 1.0 M at 25° C.

The inventive methods (in particular the method used for preparing thelignin-derived target compounds according to the invention) thus involvea sulfonation step (e.g. step (5)) wherein at least one sulfonyl groupis introduced into the precursor compounds (preferably (hydro-)quinones)obtained from the previous step (e.g. step (4)).

Thereby, the inventive method may preferably yield sulfonated(optionally lignin-derived) quinones (including benzo, anthra- andnaphthoquinones as described in greater detail below), which areespecially attractive target compounds in accordance with the presentinvention due to their reversible and fast (optionally proton-coupled)electron transfer processes. In aqueous solution, quinones typicallyundergo fast two-electron reduction with or without proton transferdepending on pH. Under acidic conditions, quinones are thus typicallyreduced to hydroquinones, whereby at least one oxo-group bound to thearomatic ring of the quinone is converted into a hydroxyl-group.

The sulfonated (optionally lignin-derived) redox active target compoundsdescribed herein as well as the compositions comprising the same areenvisaged as electrolytes. Preferably, such compounds or compositionsare thus provided in the form of an electrolyte solution for redox flowbattery applications. Therefore, (optionally lignin-derived) targetcompounds or compositions comprising the same are preferably dissolved(or suspended) in a suitable solvent (e.g. water) to yield anelectrolyte solution for use in redox flow batteries. Accordingly,compositions may be provided in solid or liquid form. It is generallyconceivable to employ liquid compositions without prior dissolution inredox flow batteries, however, generally the liquid composition will bedissolved in a suitable solvent to yield an electrolyte solution thatfor use in redox flow batteries.

Process

In accordance with the above, an exemplary method for providing theinventive sulfonated target compounds may include the steps as describedin the following, using lignocellulosic material as a starting material.The method can be performed using any suitable starting material asdescribed herein. However, the use of lignocellulosic material may havethe advantage that the precursor compounds obtainable from step (4) (anyone of sub-steps (4.1)-(4.5)) preferably already comprise C₁₋₆ alkoxysubstituents (in particular methoxy or ethoxy groups), which may conferfurther desired properties in particular when the target compounds areintended for use as redox flow battery electrolytes. The compoundsobtained from step (4) that are further sulfonated in step (5) of theinventive method may thus advantageously carry C₁₋₆ alkoxy groups assubstituents. The derivatization step (6) may be employed to introducefurther substituents of interest. It is however also possible tointroduce C₁₋₆ alkoxy groups afterwards into precursor compoundsobtained from starting materials other than lignocellulosic material(e.g. using a derivatization reaction as described herein).

Accordingly, in a first step (1), a lignocellulosic material may beprovided (sub-step (1.1)) and subjected to pulping (sub-step (1.2)). Thelignocellulosic material may be provided in chopped form (e.g. aswoodchips) and may for instance derived from wood of low silica andresin content, such as beech (or any other wood described above).

In sub-step (1.2), the lignocellulosic material may be subjected to apulping process as described herein. Typically, said pulping process maybe a Kraft process or a sulfite process as described above. In the Kraftprocess, the lignocellulosic material is typically wetted and pre-heatedwith steam, and cooked (e.g. under at least 4 bar for 3-5 hours at 150°C. or more, e.g. 170 to 180° C.) in an aqueous alkaline solution (e.g.sodium hydroxide) comprising a suitable Kraft pulping reactive agent(such as a sulfide salt, a sulfhydryl compound or salt, and apolysulfide salt, additionally, a sulfate salt may be added). Such asolution may be “white liquor” containing sodium hydroxide and sodiumsulfide. The Kraft process typically yields “Kraft lignin” which may befurther sulfonated to obtain “sulfonated Kraft lignin”. However, otherpulping processes as described herein may be applied as well. Inparticular, the sulfite process may be employed. In the sulfite process,lignocellulosic material is typically wetted and preheated with steam,and cooked (e.g. under at least 4 bar for 4-6 hours at 120° C. to 170°C., e.g. 130° C.-160° C.) in an aqueous, typically acidic solution oflow pH (e.g. pH 1-5) comprising a sulfite or bisulfite agent.

The pulping process preferably disintegrates wood into its componentslignin, cellulose and hemicellulose, which may be separated in asubsequent step.

In sub-step (1.3), the pulp is separated from the process stream, toprovide at least one process stream that is substantially free fromcellulose and comprises modified lignin-derived components,hemicellulose, and the like. Separation may typically be accomplished byblowing, sieving, filtration and one or more washing steps.

Subsequently, in step (2), modified lignin-derived components may beisolated from other components of the process stream(s), e.g. by ultra-and/or nanofiltration with suitable molecular weight cut-off values(such as about 5 kDa for ultrafiltration and 0.1-5 kDa fornanofiltration).

The isolated modified lignin-derived components are then subjected tochemical decomposition in step (3), e.g. by oxidative cracking (althoughother chemical decomposition methods described herein are alsoapplicable), to break or dissociate larger molecules into their smallerfragments by dissociation of their covalent bonds. Oxidative crackingmay be effected in the presence of a suitable oxidizing agent, such asair, and a suitable catalyst. The catalyst may be a homogenous catalyst,e.g. a metal salt comprising a metal ion such as Cu(II) or Fe(III), orcomprising a metalloid component such as B(III), Si(IV) and Al(III).Chemical decomposition may be conducted at elevated temperatures(i.e. >30° C., e.g. 150° C.) but is typically performed at temperaturesthat do not induce pyrolysis of the treated materials (i.e. <350° C.).Other chemical decomposition steps as described herein may also beapplied.

In subsequent step (4), low molecular weight aromatic lignin-derivedcomponents are isolated from higher molecular weight aromaticlignin-derived components and/or other non-lignin-derived residualcomponents, e.g. by ultra- or nanofiltration (sub-step (4.1)). Theemployed ultra- or nanofilters may have a molecular weight cut-off of0.15 kDa to 1 kDa or less, eg. 0.5 kDa.

Low molecular weight aromatic lignin-derived compounds may preferably bearomatic and include one or two (non-annulated) aromatic rings,optionally joined by an aliphatic linker.

Exemplary low molecular weight aromatic lignin-derived compoundsobtainable by the inventive method include phenolic derivatives ofbiphenyl, benzylalcohol, benzaldehydes and benzoic acid, preferablyderivatives of p-hydroxy benzylalcohol, p-hydroxy benzaldehydes andp-hydroxy benzoic acid, or more preferably vanillin, guaiacol, eugenol,syringol, phenol, syringaldehyde, or derivatives thereof.

In sub-step (4.2), monocyclic compounds may be subjected to a FriedelCrafts acylation (or another suitable annulation reaction) to produceannulated bi- or tricyclic compounds (or tetra- or pentacyclic, or evenhigher n-cyclic compounds).

In sub-step (4.3), the (optionally annulated) low molecular weightlignin-derived compounds may be oxidized in the presence of an oxidizingagent, such as H₂O₂ or O₂, and a suitable catalyst. Useful catalysts inthis context include, for instance, Co(II) complexes such as(pyr)Co(II)salen, Co(3-methoxysalen) and Co(N—N-Me salpr). Thereby,preferably hydroquinone compounds (such as benzohydroquinones,napthohydroquinones or anthrahydroquinones) are obtained.

Step (4) may further involve purification of said low molecular weightaromatic lignin-derived compounds (sub-step (4.4)), e.g. bydiafiltration or extraction, optionally followed by fractionateddistillation. The low-molecular weight aromatic lignin-derived compoundsmay further be derivatized (sub-step (4.5) in order to introducechemical groups of interest. Notably, the order of sub-steps (4.1)-(4.5)may be altered in any suitable manner.

Step (4) of the inventive method preferably yields (optionallyderivatized) (hydro-)quinones that are subsequently subjected to asulfonation step (5) to introduce at least one sulfonyl (SO₃H—) group,yielding the sulfonated target compounds of the present invention. Saidsulfonated target compounds may optionally be subjected to furtherderivatization steps (step (6)) and/or purification steps (step (7)).Finally, a redox flow battery electrolyte comprising or consisting ofthe sulfonated target compounds may be provided (step (8)).

Sulfonated Lignin-Derived Target Compounds

In a further aspect, the present invention provides sulfonated(optionally lignin-derived) low molecular weight aromatic compounds anda composition comprising or (essentially) consisting of the same,optionally obtained or obtainable by the method according to theinvention.

Such target compounds (which may optionally be obtained or obtainable bystep (5) (or optionally step (6), (7) or (8)) of the inventive method)preferably comprises one, two or three aromatic (carbocyclic) ring(s).The aromatic ring(s) of the lignin-derived low molecular weight aromaticcompound is/are substituted in at least one, preferably in at least twoor more positions by a functional group, wherein two functional groupsare preferably hydroxyl or oxo, wherein at least one functional group issulfonyl. Preferred lignin-derived target compounds are described in thesection headed “Redox active compounds and compositions” above.

Particularly preferred (optionally lignin-derived) target compounds inaccordance with the present invention include quinones or hydroquinones.Specific quinones or hydroquinones in oxidized form for use with anyaspect of the invention include 1,4-benzoquinone-2,5-disulfonic acid,1,4-benzoquinone-2,6-disulfonic acid, 1,4-benzoquinone-2-sulfonic acid,1,4-naphthoquinone-2,6-disulfonic acid,1,4-naphthoquinone-2,7-disulfonic acid,1,4-naphthoquinone-5,7-disulfonic acid, 1,4-naphthoquinone-5-sulfonicacid, 1,4-naphthoquinone-2-sulfonic acid,9,10-anthraquinone-2,6-disulfonic acid,9,10-anthraquinone-2,7-disulfonic acid,9,10-anthraquinone-1,5-disulfonic acid, 9,10-anthraquinone-1-sulfonicacid, 9,10-anthraquinone-2-sulfonic acid, or derivatives or a mixturethereof.

The (optionally lignin-derived) target compounds and compositionscomprising the same are preferably redox active (as defined above), andthus particularly useful as redox flow battery electrolytes.

Redox Flow Battery

In a further aspect, the present invention provides a redox flow batterycomprising at least one sulfonated (optionally lignin-derived) targetcompound (or a composition comprising or (essentially) consisting thesame) as defined herein as a redox flow battery electrolyte.

Redox flow batteries typically comprise two parallel electrodesseparated by an ion exchange membrane, forming two half-cells.Preferably, redox flow batteries according to the invention thuscomprise (1) a first half-cell comprising a first or negative electrodecontacting a first (optionally aqueous) electrolyte solution comprisingthe first electrolyte; (2) a second half-cell comprising a second orpositive electrode contacting a second (optionally aqueous) electrolytesolution comprising the second electrolyte; and (3) a separator (or“barrier”) disposed between the first and second electrolytes.

Redox Flow Battery (Half-)Cells

The redox flow battery cell typically comprises of a first half-cellharbouring the positive electrode in contact with the first electrolytesolution (“catholyte solution”) and—separated therefrom by a suitablebarrier—a second half-cell harbouring a negative electrode in contactwith the second electrolyte solution (“anolyte solution”). Preferably,the half-cells are configured as separate reservoirs (or chambers)within the redox flow battery cell, through which the first and/orsecond electrolyte solutions flow so as to contact the respectiveelectrodes disposed in the electrolyte solution, and the separator. Eachcontainer and its associated electrode and electrolyte solution thusdefines its corresponding redox flow half-cell. The electrochemicalredox reactions of the employed electrolytes occur within thehalf-cells.

Specifically, the current invention in particular provides a redox flowbattery comprising: a first (optionally aqueous) electrolyte solutioncomprising a first (redox active) electrolyte; a first electrode incontact with said first (optionally aqueous) electrolyte solution; asecond (optionally aqueous) electrolyte solution comprising a second(redox active) electrolyte; a second electrode in contact with saidsecond (optionally aqueous) electrolyte solution; wherein one or both ofthe first and second (redox active) electrolytes comprise at least onesulfonated (optionally lignin-derived) target compound as defined herein(preferably at least one sulfonated (optionally lignin-derived)(hydro-)quinone) or a composition comprising or (essentially) consistingof the same as defined herein.

These redox flow half-cells may be composed of any preferably chemicallyinert material suitable to retain the respective electrolyte solutions.Said half-cells are connected to a power source. Further, each redoxflow half-cell chamber may be connected, preferably via suitable ducts,to at least one separate storage tank comprising the respectiveelectrolyte solution flowing through said half-cell chamber. The storagetanks contain the positive and negative active materials; the tankvolume determines the quantity of energy stored in the system, which maybe measured in kWh. The ducts may comprise transportation means (e.g.pumps) for transporting the electrolyte solutions from the storage tanksthrough the corresponding half-cell chamber.

The redox flow battery cell may further comprise control software,hardware, and optional safety systems suitably include sensors,mitigation equipment and other electronic/hardware controls andsafeguards to ensure safe, autonomous, and efficient operation of theredox flow battery. Such systems are known to those of ordinary skill inthe art.

Typically, the first redox flow battery half-cell is separated from thesecond redox flow battery half-cell by a separator (also referred to asa “membrane” herein). Said separator preferably functions to (1)(substantially) prevent mixing of first and second electrolyte; (2)reduces or prevents short circuits between the positive and negativeelectrodes; and (3) enables ion transport between the positive andnegative electrolyte chambers, thereby balancing electron transportduring charge and discharge cycles.

The separator may for instance be selected from an ion conductingmembrane or a size exclusion membrane.

Separators are generally categorized as either solid or porous. Solidseparators may comprise an ion-exchange membrane, wherein a ionomerfacilitates mobile ion transport through the body of the polymer whichconstitutes the membrane. The facility with which ions conduct throughthe membrane can be characterized by a resistance, typically an arearesistance in units of ohm-cm2. The area resistance is a function ofinherent membrane conductivity and the membrane thickness. Thinmembranes are desirable to reduce inefficiencies incurred by ionconduction and therefore can serve to increase voltage efficiency of theredox flow battery cell. Active material crossover rates are also afunction of membrane thickness, and typically decrease with increasingmembrane thickness. Crossover represents a current efficiency loss thatmust be balanced with the voltage efficiency gains by utilizing a thinmembrane.

Such ion-exchange membranes may also comprise or consist of membranes,which are sometimes referred to as polymer electrolyte membranes (PEMs)or ion conductive membranes (ICMs). The membranes according to thepresent disclosure may comprise any suitable polymer, typically an ionexchange resin, for example comprising a polymeric anion or cationexchange membrane, or combination thereof. The mobile phase of such amembrane may comprise, and/or is responsible for the primary orpreferential transport (during operation of the battery) of at least onemono-, di-, tri-, or higher valent cation and/or mono-, di-, tri-, orhigher valent anion, other than protons or hydroxide ions.

Additionally, substantially non-fluorinated membranes that are modifiedwith sulfonic acid groups (or cation exchanged sulfonate groups) mayalso be used. Such membranes include those with substantially aromaticbackbones, e.g., poly-styrene, polyphenylene, bi-phenyl sulfone (BPSH),or thermoplastics such as polyetherketones or polyethersulfones.Examples of ion-exchange membranes comprise Nafion.

Porous separators may be non-conductive membranes that allow chargetransfer between two electrodes via open channels filled with conductiveelectrolyte solution. Porous membranes are typically permeable to liquidor gaseous chemicals. This permeability increases the probability ofchemicals (e.g. electrolytes) passing through porous membrane from oneelectrode to another causing cross-contamination and/or reduction incell energy efficiency. The degree of this cross-contamination dependson, among other features, the size (the effective diameter and channellength), and character (hydrophobicity/hydrophilicity) of the pores, thenature of the electrolyte, and the degree of wetting between the poresand the electrolyte solution. Because they contain no inherent ionicconduction capability, such membranes are typically impregnated withadditives in order to function. These membranes are typically comprisedof a mixture of a polymer, and inorganic filler, and open porosity.Suitable polymers include those chemically compatible with theelectrolytes and electrolyte solutions described herein, including highdensity polyethylene, polypropylene, polyvinylidene difluoride (PVDF),or polytetrafluoroethylene (PTFE). Suitable inorganic fillers includesilicon carbide matrix material, titanium dioxide, silicon dioxide, zincphosphide, and ceria and the structures may be supported internally witha substantially non-ionomeric structure, including mesh structures suchas are known for this purpose in the art.

-   -   Separators of the present disclosure may feature a thickness of        about 500 microns or less, about 300 microns or less, about 250        microns or less, about 200 microns or less, about 100 microns or        less, about 75 microns or less, about 50 microns or less, about        30 microns or less, about 25 microns or less, about 20 microns        or less, about 15 microns or less, or about 10 microns or less,        for example to about 5 microns.

The negative and positive electrodes of the inventive redox flow batteryprovide a surface for electrochemical reactions during charge anddischarge. As used herein, the terms “negative electrode” and “positiveelectrode” are electrodes defined with respect to one another, such thatthe negative electrode operates or is designed or intended to operate ata potential more negative than the positive electrode (and vice versa),independent of the actual potentials at which they operate, in bothcharging and discharging cycles. The negative electrode may or may notactually operate or be designed or intended to operate at a negativepotential relative to the reversible hydrogen electrode. The negativeelectrode is associated with the first aqueous electrolyte and thepositive electrode is associated with the second electrolyte, asdescribed herein.

Either or both of the electrodes that carry out the electrochemicalreactions may comprise carbon or any other suitable material, e.g.carbon black, carbon nanotubes, graphene, graphite.

Electrolyte Solutions

The redox flow battery according to the invention may thus comprise (1)a first half-cell comprising a first (redox active) electrolyte,optionally dissolved or suspended in suitable solution, in contact withthe first electrode and (2) a second half-cell comprising a sulfonated(optionally lignin-derived) target compound (preferably a sulfonated(hydro-)quinone) as a second (redox active) electrolyte, preferablydissolved or suspended in aqueous solution, in contact with the secondelectrode. The first redox active electrolyte may alternatively includechlorine, bromine, iodine, oxygen, vanadium, chromium, cobalt, iron,manganese, cobalt, nickel, copper, or lead, in particular, bromine or amanganese oxide, a cobalt oxide or a lead oxide, while the second redoxactive electrolyte is selected from a sulfonated (optionallylignin-derived) target compound as described herein, preferably asulfonated (hydro-)quinone as described herein. It is also conceivablethat both the first and the second electrolyte is a sulfonated(optionally lignin-derived) target compound (preferably a sulfonated(hydro-)quinone as described herein). The first (redox active)electrolyte may function as the anolyte, and the second (redox active)electrolyte may function as the catholyte, or vice versa.

The first and/or second electrolyte is preferably provided in the formof an electrolyte solution. Thus, the first and/or second electrolyte(at least one being selected from a sulfonated (optionallylignin-derived) target compound or composition comprising the same asdescribed herein) are preferably dissolved (or suspended) in a suitablesolvent, e.g. water, methanol, ethanol, dimethylsulfoxide, acetonitrile,acetone and glycol.

Thus the redox flow battery according to the invention preferablycomprises in at least one of its half-cells an electrolyte solution(preferably comprising at least one target compound or compositiondescribed herein) which comprises an aqueous solvent system. The term“aqueous solvent system” refers to a solvent system comprisingpreferably at least about 20% by weight of water, relative to totalweight of the solvent. In some applications, soluble, miscible, orpartially miscible (emulsified with surfactants or otherwise)co-solvents may also be usefully present which, for example, extend therange of water's liquidity (e.g., alcohols/glycols). In addition to theredox active electrolytes described herein, the electrolyte solutionsmay contain additional buffering agents, supporting electrolytes,viscosity modifiers, wetting agents, and the like, which may be part ofthe solvent system.

Thus, the term “aqueous solvent system” may generally include thosecomprises at least about 55%, at least about 60 wt %, at least about 70wt %, at least about 75 wt %, at least about 80%, at least about 85 wt%, at least about 90 wt %, at least about 95 wt %, or at least about 98wt % water, relative to the total solvent. Sometimes, the aqueoussolvent may consist essentially of water, and be substantially free orentirely free of co-solvents or other (non-target compound) species. Thesolvent system may be at least about 90 wt %, at least about 95 wt %, orat least about 98 wt % water, or may be free of co-solvents or other(non-target compound) species.

One or both electrolyte solutions may be characterized as having a pH ofbetween about <0 and about >14. The pH of the electrolyte solution maybe maintained by a buffer. Typical buffers include salts of phosphate,borate, carbonate, silicate, trisaminomethane (Tris),4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES),piperazine-N,N′-bis(ethanesulfonic acid) (PIPES), and combinationsthereof. A user may add an acid (e.g., HCl, HNO3, H2SO4 and the like), abase NaOH, KOH, and the like), or both to adjust the pH of a givenelectrolyte solution as desired.

The pH of the first and second electrolyte solutions may be equal orsubstantially similar; or the pH of the two electrolytes differ by avalue in the range of about 0.1 to about 2 pH units, about 1 to about 10pH units, about 5 to about 12 pH units, about 1 to about 5 pH units,about 0.1 to about 1.5 pH units, about 0.1 to about 1 pH units, or about0.1 to about 0.5 pH units. In this context, the term “substantiallysimilar,” without further qualification, is intended to connote that thedifference in pH between the two electrolytes is about 1 pH unit orless, such as about 0.4 or less, about 0.3 or less, about 0.2 or less,or about 0.1 pH units or less.

The disclosed redox flow battery may also be characterized in terms ofits half-cell reduction potentials. Both the negative and positiveelectrode preferably exhibit a half-cell standard reduction potential. Aredox flow battery cell according to the present disclosure may exhibita half-cell potential for the negative electrode less than about +0.3 Vvs. SHE, preferably less than about +0.1 V vs. SHE. A redox flow batterycell according to the present disclosure, specifically when employingsulfonated (hydro-)quinones as described herein as redox flow batteryelectrolytes, may exhibit a half-cell potential for the positiveelectrode at least about +0 V vs. SHE, preferably at least +0.5 V vs.SHE, most preferably at least about 0.7 V vs. SHE.

The disclosed redox flow batteries may also be characterized in terms oftheir energy density. Flow batteries of the present disclosure mayoperate with an energy density of, at least between about 10 Wh/L perside and about 20 Wh/L per side, preferably between about 20 Wh/L perside and about 50 Wh/L per side, most preferably between about 50 Wh/Lper side and about 100 Wh/L per side,

Operation

In a charging cycle, electrical power is applied to the system. Thereby,the redox active electrolyte contained in the one (for instance thesecond) electrolyte solution undergoes one-or-more electron oxidationand the redox active electrolyte in the other (for instance the first)electrolyte solution undergoes one-or-more electron reduction.Similarly, in a discharge cycle one (for instance the second)electrolyte is reduced and the other (for instance the first)electrolyte is oxidized producing electrical power.

As indicated above, it is conceivable to employ different sulfonated(optionally lignin-derived) compounds (preferably sulfonated(hydro-)quinones) as the first and the second electrolyte in the redoxflow batteries according to the invention. Accordingly, the inventionthus features a redox flow battery including first and second electrodesseparated by a separator, wherein in its charged state, the redox flowbattery includes a sulfonated quinone at the first electrode and asulfonated hydroquinone at the second electrode, wherein duringdischarge, the sulfonated quinone is reduced, and the sulfonatedhydroquinone is oxidized. Specifically, the sulfonated quinone and/orhydroquinone may be dissolved or suspended in aqueous solution.

Redox Flow Battery Stacks

In some cases, a user may desire to provide higher charge or dischargevoltages than available from a single battery. In such cases, and incertain embodiments, then, several batteries are connected in seriessuch that the voltage of each cell is additive. An electricallyconductive, but non-porous material (e.g., a bipolar plate) may beemployed to connect adjacent battery cells in a bipolar stack, whichallows for electron transport but prevents fluid or gas transportbetween adjacent cells. The positive electrode compartments and negativeelectrode compartments of individual cells are suitably fluidicallyconnected via common positive and negative fluid manifolds in the stack.In this way, individual electrochemical cells can be stacked in seriesto yield a desired operational voltage.

Several redox flow batteries may be connected in series via electricallyconductive, preferably non-porous material which allows for electrontransport but prevents fluid or gas transport between adjacent cells(e.g., a bipolar plate) in a bipolar redox flow battery stack. Positiveand negative electrode compartments of each cell are preferablyconnected via common positive and negative fluid manifolds in the stack.Thereby, individual electrochemical cells can be stacked in series toyield a desired operational voltage.

The term “bipolar plate” refers to an electrically conductive,substantially nonporous material that may serve to separateelectrochemical cells in a cell stack such that the cells are connectedin series and the cell voltage is additive across the cell stack. Thebipolar plate has two surfaces such that one surface of the bipolarplate serves as a substrate for the positive electrode in one cell andthe negative electrode in an adjacent cell. The bipolar plate typicallycomprises carbon and carbon containing composite materials.

Energy Storage Systems

Redox flow battery cells, cell stacks, or redox flow batteries asdescribed herein comprising the sulfonated (optionally lignin-derived)target compounds may be incorporated in larger energy storage systems,suitably including piping and controls useful for operation of theselarge units. Piping, control, and other equipment suitable for suchsystems are known in the art, and include, for example, piping and pumpsin fluid communication with the respective electrochemical reactionchambers for moving electrolytes into and out of the respective chambersand storage tanks for holding charged and discharged electrolytes.

The storage tanks contain the redox active materials; the tank volumedetermines the quantity of energy stored in the system, which may bemeasured in kWh. The control software, hardware, and optional safetysystems suitably include sensors, mitigation equipment and otherelectronic/hardware controls and safeguards to ensure safe, autonomous,and efficient operation of the flow battery energy storage system. Suchsystems are known to those of ordinary skill in the art. A powerconditioning unit may be used at the front end of the energy storagesystem to convert incoming and outgoing power to a voltage and currentthat is optimal for the energy storage system or the application. Forthe example of an energy storage system connected to an electrical grid,in a charging cycle the power conditioning unit would convert incomingAC electricity into DC electricity at an appropriate voltage and currentfor the electrochemical stack. In a discharging cycle, the stackproduces DC electrical power and the power conditioning unit converts toAC electrical power at the appropriate voltage and frequency for gridapplications.

The energy storage and generation systems described herein may alsoinclude electrolyte circulation loops, which may comprise one or morevalves, one or more pumps, and optionally a pressure equalizing line.Hence, the energy storage system according to the invention may compriseat least one redox flow battery, a first chamber containing the first(preferably aqueous) electrolyte and a second chamber containing thesecond (preferably aqueous) electrolyte; at least one electrolytecirculation loop in fluidic communication each electrolyte chamber, saidat least one electrolyte circulation loop comprising storage tanks andpiping for containing and transporting the electrolytes; controlhardware and software (which may include safety systems); and anoptional power conditioning unit.

The energy storage and generation systems of this disclosure can alsoinclude an operation management system. The operation management systemmay be any suitable controller device, such as a computer ormicroprocessor, and may contain logic circuitry that sets operation ofany of the various valves, pumps, circulation loops, and the like.

The energy storage systems of the present disclosure are preferablysuited to sustained charge or discharge cycles of several hourdurations. For example, redox flow batteries comprising the sulfonated(optionally lignin-derived) compounds of the present invention may becapable of retaining at least about 70% efficiency when subjected to 10charge/discharge cycles. As such, the systems of the present disclosuremay be used to smooth energy supply/demand profiles and provide amechanism for stabilizing intermittent power generation assets (e.g.,from renewable energy sources). It should be appreciated, then, thatvarious embodiments of the present disclosure include those electricalenergy storage applications where such long charge or dischargedurations are valuable. For example, non-limiting examples of suchapplications include those where systems of the present disclosure areconnected to an electrical grid include, so as to allow renewablesintegration, peak load shifting, grid firming, baseload power generationconsumption, energy arbitrage, transmission and distribution assetdeferral, weak grid support, and/or frequency regulation. Cells, stacks,or systems according to the present disclosure may be used to providestable power for applications that are not connected to a grid, or amicro-grid, for example as power sources for remote camps, forwardoperating bases, off-grid telecommunications, or remote sensors.

Assembly

Also disclosed herein is an assembly which is provided for conductingthe inventive method and in particular steps (1.3) to (5), which are notpart of a conventional pulp and/or paper manufacturing plant. Withregard to step (1.3), pulp separation from the process streamoriginating from the pulping process (step (1.2)) is conducted as a coreactivity to obtain the target product of a conventional pulp and/orpaper manufacturing plant. However, the separation of the process streaminto at least two partial process streams as optionally devised in step(1.3) is not part of a known pulp and/or paper manufacturing plant.Hence, the assembly disclosed herein comprises (i) optionally a streamseparator, (ii) an isolation unit, (iii) a decomposition unit, and (iv)a separation unit.

The provision of the process stream in step (1.3) to provide partialprocess streams in step (1.3(b)) is preferably conducted in a streamseparation unit, comprising mechanical and/or pneumatic means known inthe art. The isolation of the modified lignin may be conducted in anisolation unit, comprising, for example, means for conducting(ultra-)filtration, extraction and countercurrent flow.

Preferably, the stream separator of the assembly facilitates that thesubstantially pulp-free process stream of step (1.3) is divided into atleast two partial process streams. By means of the stream separator, theratio of the at least two partial process streams may be controlled,which streams may be supplied to different further processing.Typically, the fraction of modified lignin-derived components of one ofthe partial process streams is not isolated. Instead the streamcomprising the original content of modified lignin is forwarded to acombustion and recovery unit. Using some of the fraction of modifiedlignin-derived components as an internal energy fuel for the energysupply for the pulp and/or paper manufacturing plant. Additionally,residual reactive agents are regained, e.g. from the black or brownliquor or from organic solvents. These reactive agents are typicallysalts, which withstand temperatures of, for example, at least 500° C.,or even at least 750° C., or even at least 1000° C. During combustion,e.g. sodium sulfate may be reduced to sodium sulfide by the organiccarbon in the mixture, which may be reused in the pulping process. Incontrast, the organic material, which serves as internal fuel, such asthe modified lignin, hemicellulose, residual cellulose and/or fragmentsthereof, are burned at temperatures of, for example, at least 500° C.,or even at least 750° C., or even at least 1000° C.

The combustion and recovery process is more frequently employed inplants operating according to the Kraft process. Therein, excess blackliquor typically contains about 15% (w/w) solids and may be concentratedin a multiple effect evaporator. After said concentration, the blackliquor is typically enriched to about 20-30% (w/w) solids. At such aconcentration of solids, a naturally comprised soap called rosin soaprises to the surface and is skimmed off.

The collected soap is further processed to tall oil. Removal of the soapimproves the combustion operation. Soap-depleted black liquor with about20-30% (w/w) solids is be called weak black liquor. It may then befurther evaporated to 65% or even 80% solids, which may be called “heavyblack liquor”, and may be burnt in a recovery boiler to provide energyand to recover the inorganic chemicals for reuse in the pulping process.Concentrated black liquor is usually appreciated for its large heatingvalue (about 12.000 to 13.000 Btu/dry Ib). The heat released from thecombustion is used to generate high pressure and power. Therefore, thehigh pressure steam may be fed to turbogenerators, reducing the steampressure for the plant use and generating electricity. Some of the heatreleased and part of the reducing value in black liquor is used to drivethe pulp and/or paper production plant's reactive agent recoveryoperation.

Thus, the fraction of modified lignin-derived components of the processstream coming from step (1) of the inventive method is typically animportant fuel for paper and pulp manufacturing plant as it contributesheavily to a pulp and/or paper production plant's energyself-sufficiency. Moreover, the pulp and paper industry traditionallyhas a highly efficient infrastructure for growth, harvesting, transport,and processing of forest materials. For example, Kraft operations arehighly integrated and depend on the (modified) lignin fraction from woodas a fuel to operate the incredibly expensive chemical recovery boilersthat are the heart of their operation. In the past, diverting this fuelsource to other uses would have required the pulping operation tosupplement its energy needs by purchasing natural gas or coal,potentially upsetting the plant's economics. Therefore, the Kraftprocess in contrast to the sulfite process essentially did not provide asource of lignin-derived raw material.

However, modern pulp and/or paper production plants, including suchrunning under the Kraft process, become more and more energy efficient.Additionally, bark and wood residues may be burned in a separate powerboiler to generate steam. Said overflow in energy sources available to amodern pulp and/or paper manufacturing plant may provide a sufficient“safety margin” to divert lignin-derived combustible material while theplant remains self-sufficient in terms of energy supply.

The “safety margin” of overflow modified lignin available form modernpulp and/or paper production plants may be even larger considering thefact that high solid contents in the concentrated (black) liquor havethe typical drawback of resulting in higher viscosity and precipitationof solids in the ducts and the combustion and recovery unit. Thisprecipitation leads to adverse plugging and fouling of equipment, whichhas to be preferably avoided. Thus, controlling the isolation of thefraction of modified lignin-derived components, e.g. also by means ofthe stream divider of the inventive assembly, and thereby reducing themodified lignin load in the process stream supplied to the combustionand recovery unit, may advantageously contribute to avoid such adverseplugging and fouling of equipment.

In this regard, the inventive assembly provides means to balance theneeds for energy supply to the Kraft process on the one hand and thediverting of lignin and derivatives thereof on the other hand. First,the flexible control of the diverting means allows to direct exactly theshare of the process stream to the generation of electricity and/orsteam, which is actually needed to run the pulp and/or papermanufacturing plant. Thereby, modified lignin-derived components notrequired in combustion may entirely be directed to other uses such asthe further processing of modified lignin according to the presentinvention. Therefore, less or even no modified lignin is wasted anymoreas fuel in excess generation of electricity and/or steam. Second, anymodified lignin or lignin-derived compound or fragment thereof, whichdoes not yield the target compound may be recycled back to the processstream feeding the energy supply of the pulp and/or paper manufacturingplant. Third, as explained herein, pulp and/or paper manufacturingplants become more and more energy efficient, thus the required modifiedlignin supply for energy providing purposes is about to shrink.Alternatively, energy losses could be mediated by using forest residuesand/or by transferring to black liquor gasification. In that scenario,the industry could continue to generate the power they need, but becauseof the higher efficiency of gas turbines, could also produce a separatesyngas stream that can in part for the generation of energy, and in partfor the production of higher-value products.

For carrying out step (3), the assembly comprises a decomposition unit,providing means to sustain elevated temperature and/or pressure, and toprovide the required reactants in solid, liquid and/or gaseous form,preferably in one reaction vessel only. Alternatively, the decompositionunit of the assembly provides a suitable electrochemical cell such as aflow cell.

For conducting step (4), the assembly comprises an isolation unitproviding means for isolating low molecular weight aromaticlignin-derived compounds, such as monomers and dimers are used herein,from higher molecular weight lignin-derived components and/or othermaterial involved in the inventive method. Preferably said means is anultra- and/or nanofiltration unit or an extraction. All ducts and/orproduct and/or process stream contacting parts are preferably made frominert materials. The preferred details of said assembly are describedherein with regard to the method, which is performed in said assembly.For example, valves and/or pumps or gravity assisting means maytypically be employed to facilitate the required flow of the streamdownwards to the next step of the inventive method.

It is even more preferred that said assembly for conducting the requiressteps further comprises (v) optionally an annulation unit, (vi) anoxidizing unit, (vii) a derivatization unit and (viii) optionally apurification unit. Therein, typically step (4.2) is conducted in anannulation unit, step (4.3 (a)-(c)) in an oxidizing unit, and step (5)and step (6) in a derivatizing unit. The preferred requirements for suchassembly units may be derived from the conditions and characteristics ofthe method steps described herein, which are performed in said assemblyunits.

Preferably, said assembly is directly connected to a conventional pulpand/or paper production plant. However, in an alternative embodiment,the apparatus is not directly associated or attached with theconventional pulp and/or paper manufacturing plant. Instead. The processstream originating from step (1), e.g. of a conventional pulp and/orpaper manufacturing plant, is collected and then transferred to adistinct apparatus suitable to conduct the steps (2) to (5) andoptionally (6). Yet, in the context of the present invention, a directintegration of the apparatus suitable to conduct the steps (2) to (5)and optionally (6) is preferred, as such direct integration provides fora flexible separation of the lignin-derived compounds in the processstream depending on the energy needs and further parameters of the pulpand/or paper manufacturing plant.

In a further aspect of the present invention, a method is provided forapplying a pulp and/or paper manufacturing process using the pulpingprocess by a plant, wherein the plant is equipped with an assemblyaccording to the present invention. Accordingly, said method refers tomodifying an existing pulp and/or paper manufacturing plant, workinge.g. under the Kraft or sulfite process, wherein the plant is providedwith the assembly according to the present invention. This may be ofparticular benefit, as an existing plant is thereby upgraded to providepotentially simultaneously (i) conventional pulp and/or paper, (ii)energy supply from lignin combustion to run the plant in a preferablyself-sustaining manner, and (iii) intermediates of fine chemicals orfine chemicals such as redox active compounds based on the otherwiseby-product of modified lignins. The such upgraded plant may beversatilely operated depending on actual demand for pulp, energy or finechemical. Hence, this method significantly adds flexibility andappreciation to the existing pulp and/or paper manufacturing plant.

DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 show steps (5) (sulfonation) and following steps of anexemplary method according to the invention.

EXAMPLES

The examples shown in the following are merely illustrative and shalldescribe the present invention in a further way. These examples shallnot be construed to limit the present invention thereto. The followingpreparations and examples are given to enable those skilled in the artto more clearly understand and to practice the present invention. Thepresent invention, however, is not limited in scope by the exemplifiedembodiments, which are intended as illustrations of single aspects ofthe invention only, and methods, which are functionally equivalent arewithin the scope of the invention. Indeed, various modifications of theinvention in addition to those described herein will become readilyapparent to those skilled in the art from the foregoing description,accompanying figures and the examples below. All such modifications fallwithin the scope of the appended claims.

Example 1: Preparation of Low Molecular Weight Aromatic Lignin-DerivedCompounds by Cracking and Reduction by a Nickel Catalyst

Reductive cracking of a modified lignin-derived component according tostep (E.2) of the inventive method may for example be carried out bymeans of a catalyst comprising nickel, e.g. supported on activatedcarbon (Ni/C). The catalysts are typically prepared by anincipient-wetness impregnation method and further treated by acarbothermal reduction method known in the art.

Herein, nickel nitrate(II) hexahydrate [Ni(NO₃)₂ 6H2O] is used andoptionally added into water in a beaker known in the art. The solutionis then stirred, e.g. for at least 30 min, to prepare an impregnationstock solution. Activated carbon having a water absorption capacity oftypically above 1.8 mL g⁻¹ is added into the solution and the beaker maythen covered by a culture dish to keep the sample wet for a prescribedtime, preferably more than 12 h, more preferably 24 h. The sample isthen dried at a temperature above 80° C., e.g. 120° C. overnight. Theactual reduction is carried out in a container such as a preferablyhorizontal furnace in a flow of inert gas such as N₂. The flow is, e.g.,10 mL min⁻¹ or more, preferably 30 mL min⁻¹ or more. The reductiontemperature preferably reaches at least 400° C., preferably 450° C.,e.g. over set time period such as at least 30 min, preferably at least60 min. The temperature for conducting the reduction is maintained at450° C. for at least 1 h, more preferably for at least 2 h. TheNi/SBA-15 catalysts are reduced at 550° C. for 2 h. The Ni/Al₂O₃catalyst is reduced at 700° C. for 2 h. The metal loading for eachnickel- and copper-based catalyst is 10% (w/w) relative to the support.Herein, birch sawdust serves as lignocellulosic material and is treatedwith the ethanol-benzene mixture (v/v ratio 1:2) for 12 h. The treatedbirch sawdust, solvent (m/v 1:20), and catalyst (w/w 20:1) are placed inan autoclave reactor. The reactor is sealed and purged with Ar 4 to 6times to expel air. Then, the reducing reaction is conducted at 200° C.at a stirring speed of at least 300 rpm, preferably 500 rpm. When thedesired reaction time (usually 2 to 10 h) is reached, the reactor iscooled to ambient temperature before sampling.

Typically, the reaction generates 4-propylguaiacol and 4-propylsyringolas major products, together with minor alkene-substituted4-propylguaiacol and 4-propylsyringol, as determined by standard gaschromatography. The compounds are isolated according to step (F),preferably by extraction.

Example 2: Preparation of Monomeric Aromatic Lignin-Derived Moleculesfrom Lignosulfonate of a Sulfite Process by Electrooxidation

Lignosulfonate is provided by step (D) according to the presentinvention. Thereof, a 1 M aqueous NaOH solution is prepared, comprising1% (W/W) lignosulfonate. Said solution is subjected to anelectrooxidation according to step (E.3). Therein, the solution isemployed as anolyte. A 1 M aqueous solution is employed as katalyte. Aflow cell with a flow rate of 250 ml/min is used. Electrolysis isallowed to take place galvanostatically for 8 h applying current of 1mA/cm². A typical resulting voltage is 1,4 V. The voltage curvetypically is asymptotic and the solution changes preferably color frombrown to dark brown.

Samples of the solution are taken every hour over a time span of 8 h andsubsequently examined photometrically. Thereof, an absorption profiletypical for ortho-benzoquinone is determined. Hence, a lower molecularweight aromatic lignin-derived compound, quinone compound, is preparedby said method.

Said compound is then isolated according to step (F) of the presentinvention. Therefore, said compound is extracted by dichloromethane andsubsequently subjected to cycles of charging and discharging processesin a flow cell. The voltage curve shows that the compound is redoxactive, which may be reversibly electrolyzed.

Example 3: Preparation of an Annulated Quinone Compound by aFriedel-Crafts Acylation

Vanillin as a low molecular weight aromatic lignin-derived compound isprovided by step (F) according to the present invention. Said compoundis further annulated according to step (G) and oxidized according tostep (H) according to the present invention in five steps as follows:

(i) Synthesis of 4-(benzyloxy)-3-methoxybenzaldehyde (2)

Vanillin (1) (1.0 eq.) and benzyl chloride (1.2 eq.) are dissolved inN,N-dimethylformamide and potassium iodine (0.5 mol %) is added.Afterwards potassium carbonate is added and the reaction is stirredabove 60° C., preferably between 60 to 120° C. for at least 1 h,preferably 1 to 8 h. After completion of the reaction, the solution isdiluted with distilled water and extracted with an appropriate solvent.The organic phase is washed with brine and the product is then isolatedfrom the organic phase.

(ii) Synthesis of 4-(benzyloxy)-3-methoxybenzoic acid (3)

A mixture of 1,2-dimethoxyethane and potassium hydroxide (5 to 20 eq.)is purged with oxygen and the calculated amount of isolated product 2(1.0 eq.) is added. After the absorption of oxygen ceases, the mixtureis diluted with distilled water and neutral organic products areextracted with an appropriate solvent. The aqueous layer is acidifiedand the acidic organic products are extracted with an appropriatesolvent. Product 3 is isolated from the organic layer.

(iii) Synthesis of 4-(benzyloxy)-3-methoxybenzoyl chloride (4)

Isolated product 3 (1.0 eq.) is dissolved in thionyl chloride (5-20 eq.)and the mixture is stirred at 60 to 120° C. for 1 to 8 h. Aftercompletion of the reaction excess thionyl chloride is evaporated toyield desired acyl chloride 4.

(iv) Synthesis of Anthraquinones (5-7)

Aluminiumtrichloride (0.1 eq.) is added to the crude acyl chloride 4 andthe mixture is stirred for 30 to 300 min at −20 to 60° C. Aftercompletion of the reaction the mixture is carefully quenched with bicarbsolution. The product is extracted with an appropriate solvent and theorganic layer is washed with brine. The product is then isolated fromthe organic phase.

(v) Synthesis of 2,6-dihydroxy-3,7-dimethoxyanthracene-9,10-dione 8 and2,6-dihydroxy-1,7-dimethoxyanthracene-9,10-dione 9

Anthraquinone 5 or 6 are dissolved in ethyl acetate, methanol or ethanoland palladium on charcoal (1 to 30 weight %) is added. The mixture isstirred at room temperature under hydrogen atmosphere (1-10 bar). Thecatalyst is filtered off and the product (9) is isolated from themixture.

The product is then characterized by spectrographic means, and providedas redox active compound according to the present invention.

Example 4: Derivatization of (Hydro-)Quinones Example 4.1 Reduction ofDimethoxy Benzoquinone

23.2 g of sodium dithionite (0.134 mol, 1.32 eq.) was added to thesuspension of 17.0 g (0.101 mol, 1.0 eq.)2,6-dimethoxycyclohexa-2,5-diene-1,4-dione in 100 mL H₂O. After 2 hstirring at room temperature the precipitate was filtered off and driedin the air to give 15.85 g (0.093 mol, 92% yield) of2,6-dimethoxybenzene-1,4-diol as a white solid.

Example 4.2: Oxidation of Methoxy Benzohydroquinone

1.4 g of catalyst Cu/AlO(OH) was added to a solution of 8.2 g (0.059mol) 2-methoxy-1,4-dihydroxybenzene in 250 mL ethyl acetate, and thereaction mixture was stirred at room temperature for 147 h under an O₂atmosphere. After the conversion determined by HPLC reached 99%, thereaction mixture was filtered, and the recovered catalyst was washedwith ethyl acetate (100 mL×3). The filtrate was collected and solventwas removed in vacuo to give 7.66 g (0.055 mol, 95% yield) of2-methoxycyclohexa-2,5-diene-1,4-dione as a yellow-brownish solid.

Example 4.3: Acetylation of Methoxy Benzohydroquinone

8.24 g (0.059 mol, 1.0 eq.) of 2-methoxybenzene-1,4-diol was weighedinto a 250 mL reaction flask equipped with a reflux condenser. 60 mL ofdichloroethane and 15 mL (0.159 mol, 2.7 eq.) of acetic anhydride wereadded. 12 mL (0.096 mol, 1.63 eq.) of boron trifluoride ether solutionwas then slowly added at room temperature with stirring. The reactionmixture was heated to 90° C. for 20 hours. The mixture was cooled to 60°C., 30 mL H₂O was added followed by 10 mL HCl (6 M). The resultingmixture was heated to 100° C. for 30 min, cooled down and extracted withethyl acetate (150 mL×3). The combined extracts were washed sequentiallywith H₂O (100 mL), saturated sodium bicarbonate (100 mL) and H2O (100mL) and then dried with anhydrous sodium sulfate. The solvent wasremoved in vacuo to give a brown solid residue, which was washed withmethanol to give 7.49 g (0.041 mol, 70% yield) of1-(2,5-dihydroxy-4-methoxyphenyl)ethan-1-one as a beige solid.

Example 4.4 Addition of Isonicotinic Acid to Benzoquinone

2.16 g (0.02 mol, 1.0 eq.) of p-benzoquinone was suspended in 6.4 mL ofacetic acid. 2.46 g (0.02 mol, 1.0 eq.) of nicotinic acid was added andthe mixture was stirred for 2 h at rt. The resulting dark mixture wasdiluted with 3 mL of water and treated with 6.6 mL of HCl (6 M). Oncooling, solid precipitated which was filtered off and dried overnightat 60° C. to give 3.13 g (0.012 mol, 59% yield) of3-carboxy-1-(2,5-dihydroxyphenyl)pyridin-1-ium chloride as an yellowsolid.

Example 4.5 Sulfonation of Anthraquinone

A solution of anthraquinone was heated (180° C.) in a solution of20%-40% SO₃ in concentrated sulfuric acid (oleum), resulting in amixture of sulfonated anthraquinones. The crude mixture was poured ontoice and partially neutralized with calcium hydroxide. Subsequently, themixture was filtrated and concentrated to yield the final product.

Example 4.6: Sulfonation of Hydroquinone (1,4-Dihydroxybenzene)

A solution of hydroquinone was heated (80° C.) in a solution of 20%-40%SO₃ in concentrated sulfuric acid (oleum), resulting in a mixture ofsulfonated hydroquinones. The crude mixture was poured onto ice andpartially neutralized with calcium hydroxide. Subsequently, the mixturewas filtrated and concentrated to yield the final product.

Example 4.7: Sulfonation of 1,4-Dihydroxy-2,6-dimethoxybenzene

A solution of hydroquinone was heated (80° C.) in a solution of 20%-35%SO₃ in concentrated

sulfuric acid (oleum), resulting in a mixture of sulfonated1,4-dihydroxy-2,6-dimethoxybenzenes. The crude mixture was poured ontoice and partially neutralized with calcium hydroxide. Subsequently, themixture was filtrated and concentrated to yield the final product.

Example 4.8: Sulfonation of 2-Methoxyhydroquinone

A solution of 2-methoxyhydroquinone was heated (80° C.) in a solution of20%-40% SO₃ in concentrated sulfuric acid (oleum), resulting in amixture of sulfonated 2-methoxyhydroquinones. The crude mixture waspoured onto ice and partially neutralized with calcium hydroxide.Subsequently, the mixture was filtrated and concentrated to yield thefinal product.

Example 5: Model Compounds from the Modification Reaction ofBenzoquinones Paired with Sulfonated Anthraquinone in an Organic RedoxFlow Battery

Table 4 shows three examples for pairings that were used in a fullyorganic redox flow battery that were achieved by the modification ofquinones. Example A shows a pairing of a sulfonated benzohydroquinonethat was achieved by a double substitution reaction with sulfur trioxideand a sulfonated anthraquinone that was also achieved by a doublesubstitution reaction with sulfur trioxide. Example B shows a glycinsubstituted mono methoxy benzohydroquinone that was achieved by thenucleophilic attack of an glycin to the methoxy benzoquinone paired withthe sulfonated anthraquinone. In example C a isonicotinic acidsubstituted benzohydroquinone is paired with the same anthraquinone. Theisonicotinic acid was introduced by nucleophilic attack as well.

TABLE 4 Pairings for modified products in a fully organic redox flowbattery A

OCV = 0.8 V B

OCV = 1.0 V C

OCV = 0.55 V

1. A redox flow battery comprising at least one sulfonated and optionally further derivatized low molecular weight aromatic compound, wherein said compound corresponds in structure to Formula (X), (XI), (XII), (XIII), (XIV) or (XV):

wherein each R¹, R², R³ or R⁴ is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆ alkenyl, linear or branched, optionally substituted, C₁₋₆ alcohol, linear or branched, optionally substituted, C₁₋₆ aminoalkyl, linear or branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally substituted, C₁₋₆ alkoxy, linear or branched, optionally substituted, C₁₋₆ aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO₃H), provided that (i) at least three of R¹-R⁴ are SO₃H or (ii) provided that at least one of R¹-R⁴ is SO₃H and at least one of R¹-R⁴ is hydroxy or C₁₋₆ alcohol;

wherein each R¹, R², R³, R⁴, R⁵ or R⁶ is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆ alkenyl, linear or branched, optionally substituted, C₁₋₆ alcohol, linear or branched, optionally substituted, C₁₋₆ aminoalkyl, linear or branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally substituted, C₁₋₆ alkoxy, linear or branched, optionally substituted, C₁₋₆ aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO₃H), provided that (i) at least three of R¹-R⁶ are SO₃H or (ii) provided that at least one of R¹-R⁶ is SO₃H and at least one of R¹-R⁶ is hydroxy or C₁₋₆ alcohol;

wherein each R¹, R², R³, R⁴, R⁵, R⁶, R⁷ or R⁸ is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆ alkenyl, linear or branched, optionally substituted, C₁₋₆ alcohol, linear or branched, optionally substituted, C₁₋₆ aminoalkyl, linear or branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally substituted, C₁₋₆ alkoxy, linear or branched, optionally substituted, C₁₋₆ aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO₃H), provided that (i) at least three of R¹-R⁸ are SO₃H or (ii) provided that at least one of R¹-R⁸ is SO₃H and at least one of R¹-R⁸ is hydroxy or C₁₋₆ alcohol.
 2. The redox flow battery according to claim 1, wherein said redox flow battery comprises a first (optionally aqueous) electrolyte solution comprising a first (redox active) electrolyte; a first electrode in contact with said first (optionally aqueous) electrolyte solution; a second (optionally aqueous) electrolyte solution comprising a second (redox active) electrolyte; a second electrode in contact with said second (optionally aqueous) electrolyte solution; wherein one or both of the first and second (redox active) electrolytes comprise the at least one sulfonated (and optionally further derivatized) low molecular weight aromatic compound.
 3. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound corresponds in structure to Formula (X) or (XI), and wherein R¹ and R⁴ are independently selected from H and SO₃H; R² is selected from H, OH, C₁-C₆ alcohol, and SO₃H; and R³ is selected from H, OH and C₁-C₆ alcohol.
 4. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound is characterized by one of the following: a) R⁴ is SO₃H; b) R⁴ is SO₃H, R³ is methoxy; c) R⁴ is SO₃H, R² and R³ are methoxy; d) R¹ and R⁴ are SO₃H; e) R¹ and R⁴ are SO₃H, R³ is methoxy; or f) R² and R⁴ are SO₃H, and R³ is methoxy.
 5. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound corresponds in structure to Formula (XII) or (XIII), wherein R¹ and R² are independently selected from H, OH and C₁-C₆ alcohol; and R³-R⁶ are independently selected from H and SO₃H.
 6. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound corresponds in structure to Formula (XIV) or (XV) and wherein R¹, R² and R⁴ are independently selected from H, OH and C₁-C₆ alcohol; and R³, R⁵-R⁸ are independently selected from H and SO₃H.
 7. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound is characterized by one of the following: a) R¹ is SO₃H; b) R² is SO₃H; R¹, R³ and R⁴ are OH; c) R⁶ is SO₃H; R¹ and R⁴ or R¹, R² and R⁴ are OH; d) R² and R⁶ are SO₃H; R¹ and R⁴ or R¹, R³ and R⁴ are OH; e) R³ and R⁶ are SO₃H; R¹, R² and R⁴ are OH; f) R² and R⁷ are SO₃H; or g) R¹ and R⁴ are SO₃H; wherein each of the other of R¹-R⁸ is/are SO₃H, hydroxy, C₁-C₆ alcohol, or H.
 8. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound is selected from a sulfonated compound according to Table 1, 2 or
 3. 9. The redox flow battery of claim 8, wherein the sulfonated low molecular weight aromatic compound is selected from compounds 15 and 16 (Table 1), compounds 66-85 (Table 2) and compounds 293-400 (Table 3).
 10. A redox flow battery comprising a composition comprising at least two sulfonated low molecular weight aromatic compounds, wherein said compounds independently correspond in structure to Formula (X), (XI), (XII), (XIII), (XIV) or (XV):

wherein each R¹, R², R³ or R⁴ is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆ alkenyl, linear or branched, optionally substituted, C₁₋₆ alcohol, linear or branched, optionally substituted, C₁₋₆ aminoalkyl, linear or branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally substituted, C₁₋₆ alkoxy, linear or branched, optionally substituted, C₁₋₆ aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO₃H), provided that (i) at least two of R¹-R⁴ are SO₃H, or provided that (ii) at least one of R¹-R⁴ is SO₃H and at least one of R¹-R⁴ is hydroxy or C₁₋₆ alcohol;

wherein each R¹, R², R³, R⁴, R⁵ or R⁶ is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆ alkenyl, linear or branched, optionally substituted, C₁₋₆ alcohol, linear or branched, optionally substituted, C₁₋₆ aminoalkyl, linear or branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally substituted, C₁₋₆ alkoxy, linear or branched, optionally substituted, C₁₋₆ aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO₃H), provided that (i) at least two of R¹-R⁶ are SO₃H, or provided that (ii) at least one of R¹-R⁶ is SO₃H and at least one of R¹-R⁶ is hydroxy or C₁₋₆ alcohol;

wherein each R¹, R², R³, R⁴, R⁵, R⁶, R⁷ or R⁸ is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C₁₋₆ alkyl, linear or branched, optionally substituted, C₁₋₆ alkenyl, linear or branched, optionally substituted, C₁₋₆ alcohol, linear or branched, optionally substituted, C₁₋₆ aminoalkyl, linear or branched, optionally substituted, C₁₋₆ carboxyalkyl, linear or branched, optionally substituted, C₁₋₆ alkoxy, linear or branched, optionally substituted, C₁₋₆ aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO₃H), provided that (i) at least two of R¹-R⁸ are SO₃H, or provided that (ii) at least one of R¹-R⁸ is SO₃H and at least one of R¹-R⁸ is hydroxy or C₁₋₆ alcohol; and wherein at least one of the sulfonated low molecular weight aromatic compounds is in an oxidized state according to Formula (X), (XII) or (XIV), and/or at least one of the sulfonated low molecular weight aromatic compounds is in a reduced state according to Formula (XI), (XIII) or (XV).
 11. The redox flow battery of claim 10, wherein the at least two sulfonated low molecular weight aromatic compounds are characterized by the following: (a) at least one compound according to Formula (X) and (XI); (b) at least one compound according to Formula (XII) and (XIII); and/or (c) at least one compound according to Formula (XIV) and (XV).
 12. The redox flow battery of claim 11, wherein the composition comprises (a) at least two compounds according to Formula (X) and (XI), wherein said at least two compounds are distinctly sulfonated and/or substituted; (b) at least two compounds according to Formula (XII) or (XIII), wherein said at least two compounds are distinctly sulfonated and/or substituted; and/or (c) at least two compounds according to Formula (XIV) or (XV), wherein said at least two compounds are distinctly sulfonated and/or substituted.
 13. The redox flow battery of claim 11, wherein each of the at least two compounds comprises at least three SO₃H groups.
 14. The redox flow battery of claim 1, wherein the sulfonated (and optionally further derivatized) low molecular weight aromatic compound or a composition comprising the sulfonated low molecular weight aromatic compound is obtainable by (1) providing a starting material; (2) optionally subjecting said starting material to a process suitable to obtain at least one low molecular weight precursor compound; (3) isolating and optionally modifying at least one low molecular weight precursor compound thereby obtaining at least one low molecular weight aromatic precursor compound; (4) subjecting the at least one low molecular weight precursor compound to a sulfonation reaction, wherein one or more SO₃H groups are introduced into the at least one precursor compound thereby obtaining the at least one sulfonated low molecular weight aromatic compound or the composition comprising the sulfonated low molecular weight aromatic compound.
 15. The redox flow battery of claim 14, wherein the starting material is selected from lignocellulosic material, crude oil, coal and a pure organic substance.
 16. The redox flow battery of claim 14, wherein the compound corresponds in structure to any one of Formula (X)-(XV), and/or the composition comprises compounds corresponding in structure to any one of Formula (X)-(XV).
 17. The redox flow battery of claim 14, wherein the sulfonated (and optionally further derivatized) low molecular weight aromatic compound or the composition comprising the sulfonated low molecular weight aromatic compound is dissolved or suspended in a suitable solvent to form an electrolyte solution.
 18. The redox flow battery of claim 10, wherein: (a) in Formula X and XI at least one of R¹-R⁴ is hydroxy or C₁-C₆ alcohol; (b) in Formula XII and XIII at least one of R¹-R⁶ is hydroxy or C₁-C₆ alcohol; and/or (c) in Formula XIV and XV at least one of R¹-R⁸ is hydroxy or C₁-C₆ alcohol. 